Roleplaying-Focused Classes

[Warchon]

So I came across my first Binder this week, and I was very impressed with this class--not just for having a unique mechanic, and not necessarily for power--I only gave a cursory read to the options available to them so far and it doesn't seem particularly high powered--but for the sheer flavor. Effectively changing class features every day sounds like a lot of fun, but more importantly (to me) having the potential to have an in-game effect change your roleplaying methods every day is really neat.
It's almost like the class was designed, not to fill a niche in the type of characters players want, but directly to encourage deep and thorough roleplaying and party interactions.
Are there any other classes that are similarly built for RP?

Note: I realize this is a really broad question, and there's no end of 'flavorful' or 'aggressively unique' classes that will fit the bill. I'm fine with that--if you found "Fighter" to be an aesthetically appealing class and it got you into the story, great! I'd love to hear why. Specifically what I'm looking for though is actual gameplay mechanics built in to a class that help bring about a more engaging character.

[flappeercraft]

Really I think that all classes can be RP'd in equal amounts. A Paladin as a moral compass, the book worm wizard, the super disciplined monk, the fighter who fights for the sake of learning more combat styles and improving. All of those are common archetyped and are frequentlt considered the stereotypical ones and the ones that lack depth but what people don't realize is that if they lack depth it's not because of the class itself but because they are considered the common compared to a binder so they feel less unique.

[Venger]

Definitely agree about binder. powerwise it's comfortably a 3. 2 if you have access to zceryll.

I'd nominate totemist and incarnate as also being very rp-rich characters that open up a lot of doors. like you said, you can rp any character class any way you like, but these push you in a slightly different direction than the generic tolkien ripoff of most of the rest of the base classes and are very supportive of an american indian or japanese archetype. the same way you change vestiges every day, they change melds, and in my experience I like having the characters revere the creatures they draw power from, or the people the melds are inspired by to inform their personality.

[CMagnum]

If you like the ability to change your powers on a daily basis I think you might find the chamelion class to be lots of fun. Lots of flexibility and since changeling is the obvious racial choice you have limitless personalities you can portray.
I really enjoyed playing an archivist, a knowledge seeker who was constantly going to libraries to increase his knowledge of the world and who was able to answer almost any question due to his high knowledge skills.
I guess it depends on what you are interested in portraying. I've had fun with barbarians, wizards and everything in between. I find it comes down to backstory and character development. The more you invest in a character the more you will get out of them.
P. S. Don't be afraid to have your character flawed (not necessarily for feats but it's an option), you might be surprised at how much having done irrational fear or a dominating personality can be taken in role playing.

[Psyren]

Pathfinder has the Medium which is very similar, but gives you more general spellcasting and combat abilities as rewards for your pacts rather than the more individualized vestige powers. PF also has a third-party class (the Pactmaker) which is basically an update of the 3.5 Binder with some new bells and whistles, and whose chassis is backwards compatible with the existing vestiges. Like the Binder itself, these two work very well as the "5th man" of an existing party that can change its abilities each day to what the party needs most, with the drawback occasionally having to deal with foreign influences.

Another 3.5 class that mingles mechanics and roleplay is the Wu Jen from Complete Arcane/Oriental Adventures, which lets you apply free metamagic to some of your spells provided you maintain a series of "taboos" on your behavior. For this class, rather than having to act a certain way, the taboos force you not to act a certain way.

Both 3.5 and PF also have Vows, which give various rewards to your character in exchange for restrictions on behavior or less-than-convenient penalties. In PF these are only open to users of ki, which typically means monks, ninjas, and some flavors of paladin or oracle. Paladins also have special vows just for them that give them additional or modified codes of conduct to self-enforce.

[Troacctid]

Cataclysm Mage and Master Inquisitive spring to mind. Both classes have some interesting roleplaying elements baked in.