First things first: here. Use it, love it. It's pretty, and useful; format is always nice, and elegant for an attempt such as this.

Now, on to the meat of the business: Swashbuckler was always meant to be a class featuring bravado, daring, light armor but superb fighting skill. A cursory examination of your fix brings that into perspective quite well, drawing on things from the Rogue without eclipsing its potential (mostly with Precise Strike) and evidently throwing Duelist out of the window (never a bad thing, actually!)

Bit by bit:
Quote Originally Posted by RaveingRonin View Post
Special Abilities Removed:
Removed Grace +n (Have a good Ref save, no need for that feature)
Removed Improved Flanking (useless in general)
Removed Dodge Bonus (worse then useless)
Removed Wounding+Weakening Critical (no longer fits)
Removed Lucky (get a luck feat *******)
I agree with Grace and the switch from Dodge bonus to Canny Defense; it allows for a Int-based warrior other than a Warblade. Lucky...well, you might get a luck feat, but the Swashbuckler is a bit feat-starved; you may wanna fix that.

Improved Flanking and Wounding/Weakening Critical...now this is something I definitely would have kept. Think: Precise Strike requires you wielding a finessable piercing weapon AND either deny your Dex bonus to AC or flank. Increasing flank bonuses would be a perfect way to reinforce the idea of a flanking character, specially because you aren't granting it another method (no invisibility, feint is still a standard action). Besides, even if you only add a +1/+2 to the attack bonus via Imp. Flank, since it's a class ability and not a feat, it adds up really quick. It allows you to land more hits, land more Precise Strike hits, and crank up the damage real quick.

Wounding/Weakening Critical is something I would have left as an option along with Find the Mark, much like the Rogue special abilities starting at 10th level. You would be capable of customizing the Swashbuckler's critical hits, making the class more adept in critical hits (which was apparently the idea of the swashbuckler; wield a rapier or similar high crit-range weapon, then land as many crits as possible and land more damage that way). Find the Mark seems quite powerful, although it only adds a +1 to your crit threat range, but I feel that it could still work to your benefit to make it a set of special abilities.

Special Abilities Kept:
Acrobatic Charge at 7th level (Ignore difficult terrain in a charge)
Weapon Finesse as a bonus 1st lvl feat (Vital)
Insightful Strike at 3rd lvl (Int to bonus damage with Weapon Finesse weapons)
Acrobatic Skill Mastery lvl 13(Add Balance and Use Rope in addition to Jump and Tumble)
Slippery Mind at level 17 (Reroll Will save to avoid mind control next round)
I'd make a slight change in here. You already use your Intelligence score for damage rolls and Armor Class, but you still depend on your Dexterity for Reflex scores and attack rolls. If it were me, I'd go for a special form of Weapon Finesse, in which you'd be capable of adding your Int (instead of your Strength or Dexterity) to the attack roll, and treat the class ability as Weapon Finesse for feats and abilities that would require it. Makes the class a bit less MAD, and a bit more Int-dependant, which is always nice.

Acrobatic Charge is an ability that, unlike Improved Flank, I would remove. Now, that doesn't mean you should, since it's a very awesome ability and it allows for a very unusual fighting style, but a Swashbuckler rarely attempts a charge (it does attempt a Tumble, though). Keep it, because it's flavorful, but I don't see many Swashbucklers using a charge since unless they are invisible or have Pounce (or both!), they won't be using that tactic a lot (no Precise Strike, and that's a big downer).

Insightful Strike was an ability that was meant to be some sort of boost to the Swashbuckler's damage because they wouldn't have much Strength, but considering how the class works, it made little sense. I would collapse Weapon Finesse and Insightful Strike into a 1st level ability that replaces Str and/or Dex with Intelligence for attack rolls and damage rolls with finessable weapons, and the class ability is treated as if having Weapon Finesse. It only makes sense, and even if it may motivate a 1-level dip (something we don't want here), it gives a Swashbuckler a huge amount of power right from the start. I would advice either making Insightful Strike a replacement (replace Str and/or Dex with Int for attack and damage rolls), or in the unlikely case of addition, make it so that you add 1 point per class level (in that case, you would force a much deeper dip into the class).

Slippery Mind, though...I dunno, it's an ability that it's gotten far too late for what it's worth, and it only grants you a second saving throw on Will, which is your weakest ability. Lower it a level, perhaps make it one of the options along with Wounding/Weakening Critical and Find the Mark, so that it may enter game sooner or later. Otherwise, it won't be very powerful since you'll see less and less enchantment spells in late game (at least not more than direct damage spells).

Special Abilities added:
I'll go on this separately. I'll also make a slight alteration to the format of Canny Defense, in order to show a format which I'm quite acquainted with and that would make your class a bit more elegant.

Canny Defense: At 1st level, a swashbuckler adds his Intelligence modifier (if positive) as a dodge bonus to Armor Class when wearing light armor or no armor. This bonus increases by 1 at 5th level and again at 10th level, 15th level and 20th level, up to a maximum of +4 at 20th level. If the swashbuckler would be denied his Dexterity bonus to AC for any reason, he also loses this dodge bonus to AC.
Notice that it looks more like a rule than a footnote. I'd recommend you to do the same to the rest for purposes of elegance.

Now...I don't think I have much to say about Canny Defense. It's a double edged sword; really powerful, since you can wear light armor, and add both your Dex and your Int to AC; if both are decent enough (and considering how the class is built, you're effectively asking for Int and Dex as your good stats), you'll have a huge AC bonus by 1st level, perhaps more than a 1st level Fighter with a shield would. Of course...this isn't bad, since you're meant to be a front-line combatant, but it's a worry you might be willing to deal with. Granting full Int makes Canny Defense a very tasty reason to make a 1 level Swashbuckler dip; maybe if shuffled to level 3, it would be a bit better (then, you could move Insightful Strike to level 1, and force at least a 3-level dip if that's what people start to ask for, but then you add Precise Strike which asks for more dipping, and then...you get the idea, you hook the player on Swashbuckler). So I'd switch Canny Defense and Insightful Strike in order to make the class a bit more effective (since you'd be fighting carefully on your first few levels, then fighting with more confidence and better defense by latter levels).

The rest of the abilities will be using your current format, and merely have commentary:

-Precise Strike +1d6: Starting at 2nd level and increasing by 1d6 ever 4 levels there after (+2d6 at level 6, +3d6 at level 10, ect.), whenever the Swashbuckler attacks with a light piercing weapon or a piercing weapon that can be used with Weapon Finesse and his opponent is denied their Dexterity bonus (even if they don't normally have one) or is flanked, the Swashbuckler can execute a Precise Strike, dealing extra damage. This damage only affects creatures with discernible anatomies who are subject to critical hits. If the Swashbuckler critically hits, this extra damage is not multiplied. (Akin to rogues sneak attack, but with a slowed progression due to higher BAB and such)
So you get a maximum of 5d6 at higher level? Even though it's even more restrictive than Sneak Attack (which can be done even with a greatsword of all things!?). I dunno; you should buff Precise Strike a bit, even if you're effectively adding (if your intention is to have Insightful Strike work as this) your Int to damage, since you're forcing the character to fight with a rapier, a dagger, a spiked chain, a punching dagger, a light pick, a spiked gauntlet or a shortsword (that's basically 7 weapons with which you can do Precise Strike), AND then forcing you to either flank or deny your enemies' Dex bonus to AC (that's two restrictions, BTW). Sudden Strike has less restrictions than this and it's often considered weak, even though you can use spiked chain which means you can attemot to use this ability from range (but you'd need to be invisible for it, unless...see how flank is important? And you're throwing away Improved Flank...)

I'd personally make it 1 every 3 levels, and you can start at 2nd level; that way, you cover 2nd, 5th, 8th, 11th, 14th, 17th and 20th; a total of 7d6 points of damage, but a bit more restrictive albeit less than a regular sneak attack (though the capstone ability may change this). You'll be doing around 1-2 extra damage dice less than a rogue on average, but you have one extra attack to compensate. But, since you're focusing on a small amount of weapons (this may change with the addition of exotic weapons, but generally you're limiting yourself to 6 weapons normally, 7 with spiked chain just with core), adding more damage may eventually compensate. Don't feel scared to buff Precise Strike a bit.

The only other choice, IMO, would be to keep it as is but extend PS to all finessable weapons. No reason why light melee weapons have to be excluded just because they don't deal piercing damage.

One more thing: I would allow Precise Strike to qualify for Ambush feats. Simply no reason why it shouldn't.

-Uncanny Dodge: At 2nd level, the Swashbuckler retains his Dexterity bonus to AC even when considered flat footed.
-Evasion: At 5th level the Swashbuckler gains Evasion, as per the Rogue ability.
-Improved Uncanny Dodge: As the rogue ability, gained at 7th level.
-Improved Evasion: As the rogue special ability, gained at level 10 by the swashbuckler.
Good, great, wonderful, superb. It again fits a light-armored warrior, especially one that deals precision damage (why not be capable of evading the same kind of damage?)

-Bonus Feat: At 3rd level and every 3 levels thereafter, the Swashbuckler may pick a bonus feat selected from the fighter bonus feat list. He still must meet all prerequisites.
I was about to worry about this. Or rather, the lack of this. This is such a good relief, since it makes the swashbuckler capable of getting quite a lot of feats. Though...I would use an irregular progression for it, since you're effectively granting two feats at the same level. I would grant them at 4th level and keep it the same 3 levels, which would fit perfectly with the dead levels at 4th and 19th. I'd also expand to add Luck feats and Ambush feats, since the Swashbuckler will likely rely on both; the Swashbuckler is a smart and resourceful warrior, after all, relying on luck and tactics rather than brute force.

-Find the Mark: At 8th level, the swashbuckler increases his threat range by one whenever he uses a melee weapons with which he can apply weapon finesse. This ability stacks with other abilities that increase threat ranges. ( a keen rapier in the hands of a Swashbuckler would have a threat range of 14-20; 18-20x2 threat range=15-20+1 threat range=14-20)
-Improved Find the Mark: Level 16: As Find the Mark, but the threat range is improved by 2 rather then 1.
As I said above, I find...well, Find the Mark a very strong ability. The increase is not spectacular (you're just adding 1 to the crit range, and that's something Turbine is considering...), but I find that it makes Weakening Critical and Wounding Critical much more desirable. The problem lies when you're effectively allowing Find the Mark to stack twice, which means you're ensuring a pretty large chance to get a critical hit (and it may actually make a feat like Power Critical and other bonuses a boon to the class, since it would work as a semi-natural 20). I consider you should just make Find the Mark a single ability, re-add Wounding Critical and Weakening Critical, and make it a series of "Swashbuckler special abilities" that the character may choose; that way, even if Find the Mark will be pretty powerful, you may consider adding Wounding Critical first and starting to use your improved critical threat range and possible increased amount of critical hits to land more Constitution damage. It would also make the latter two abilities something like Crippling Strike, which is something the Rogue has naturally.

-Deflect Arrows: At level 11, the swashbuckler may use any weapon that falls under the purview of Weapon Finesse to deflect ranged attacks. This ability functions just as the feat, but the swashbuckler uses a weapon as opposed to his empty hands.
Eh...I dunno. Deflect Arrows doesn't cut it like an useful ability. Especially at that level; why level 11th? Monks get it at level 2, after all. I would have expected Snatch Arrows instead. And it's pretty limited, to boot; same as DA, but only with finessable weapons (instead of an empty hand, but you'll probably have an empty hand anyways).

-Én Guarde!: At 20th level, the Swashbuckler can assault their opponent with lightning fast strikes, more thrusts and slashes then seem possible. Using a weapon that falls under the Weapon Finesse description, the Swashbuckler may once a day use a full round action to make twice as many attacks as they would normally receive. (In short, roll two attacks for every one you would normally make).
Cool ability. Very cool ability. Very, very, very, very limited use, though. Én Garde is essentially Diamond Mind's Time Stands Still as a capstone, 1/day, non-rechargeable. That's not a very good idea, since if you have another class that can do it 1/encounter, and possibly twice or even thrice per encounter, it suddenly stops being an awesome capstone. In practice, Én Garde acts like a super-flurry, but in a very limited scope. I'd say you should make it 1/encounter.

For your consideration: a 1/encounter ability at 20th level should be a powerful ability you don't want your class to use always, but at a pivotal point in your match (same as a spell like, say, Grease or Web). A 1/day ability at 20th level should be amongst the lines of a Heal or Harm spell, something that causes a LOAD of impact and that it cannot be spammed constantly. A 1/week ability is nothing short of True Resurrection or Miracle, specially at that level. Normally, and in the line of thought of Complete Warrior, Én Garde would be a per-day ability, but after Tome of Battle, Én Garde should be a per-encounter ability; you wanna use it on your strongest enemy, probably with two weapons, beating the enemy until it's dead-dead. A per-day ability on a 20th level martial character is nothing short of Quivering Palm, and even that is questionable. The closest thing would be an actual natural 20-like attack, which means you WILL make the strike, you WILL land a crit, and you WILL activate anything that depends on a natural 20 (did someone said Vorpal?)

Finally, and for your consideration, abilities that I feel should be there:
  • More flanking options. Stuff like improbable flanking angles, for example.
  • Support for feinting. Say, the ability to make a single attack after a successful feint, or feinting as a swift action instead of standard or move; feint lasting for more than a single attack, or make feint a debuff that aids other allies. A Swashbuckler should appropriate of feint and make it a tactic that should never be denied; it also makes him all the more capable of putting Bluff to use.
  • Support for Intimidate. Demoralize opponents with a strike; purposedly botch an Intimidate check in order to goad the enemy into lowering its defense or something. You're adding Intimidate; make it useful.