Barbarian rogue

[Shadowscale]

How would one go about blending these two classes together, any good feats or prestige class intended for the crossing of these two classes?

[Troacctid]

Sneak Attack works pretty well on an ubercharger build focused on making lots of attacks with pounce. Win initiative, then tackle them while they're flat-footed, using Whirling Frenzy (http://www.d20srd.org/srd/variant/classes/classFeatureVariants.htm#rageVariantWhirlingFrenzy ) and Two-Weapon Fighting to beat their face in with as many sneak attacks as possible. If all goes well, they should drop on the first round.

[Shadowscale]

Does a prestige class designed to mix the two together exist?

[Seppo87]

You don't need a prestige class. Just select the Ferocity acf.
Get at least 13 Strength for Power Attack, then max out Dexterity. Use a spiked chain.
Dip a couple swordsage levels for Shadow Blade, useful counters/boosts and extra sneak attack.
Get Craven and Staggering Strike
Want to control the battlefield? Try Unbalancing Blow. Need more attacks? Try robilar's gambit.
Wanna charge? make sure to select the lion totem acf from CC. You don't even need feats, just buy a valorous weapon.
Want more feats? Dip hit-n-run Exoticist Fighter

There you have it, the stealthy rager. High to-hit, high damage, high ac, high initiative, good HP, good saves, good skills, can hide, can debuff, it's pretty awesome.
It's probably my favorite melee type.

A good alternative, if you want to try the intimidation route, is the avenging executioner prc.
It gives you some flavorful features along with full sudden strike progression.
If you're looking for something that mixes the scary ferocity of barbarians with backstabbing, now you have it.
As usual for intimidating mundanes, the recipe is simple. Get Never Outnumbered and Imperious Command.
Or stack multiple shaken conditions (frightful presence from Draconomicon is a decent start) then all you have to do is to kill them one by one when they are cowering

[Curmudgeon]

You don't even need feats, just buy a valorous weapon.
Valorous does very little here: the weapon deals doubles damage, but Power Attack, sneak attack, STR bonus, and everything else that's from the character and not from the weapon is unaffected.

[Seppo87]

Valorous does very little here: the weapon deals doubles damage, but Power Attack, sneak attack, STR bonus, and everything else that's from the character and not from the weapon is unaffected.
Oh, wow. I never realized that. Sorry for the inaccuracy.

[Curmudgeon]

Oh, wow. I never realized that. Sorry for the inaccuracy.
Valorous is a cheap way to rack up weapon damage on a charge. You buy a +1 Valorous weapon with a decent base damage, get it cranked up to +5 with Greater Magic Weapon, and Valorous makes it add
decent damage on every Charge attack: 4d6+10 for a Medium greatsword, for example. But that's all it does.

[Seppo87]

Valorous is a cheap way to rack up weapon damage on a charge. You buy a +1 Valorous weapon with a decent base damage, get it cranked up to +5 with Greater Magic Weapon, and Valorous makes it add
decent damage on every Charge attack: 4d6+10 for a Medium greatsword, for example. But that's all it does.well I guess one might add the Collision and Berserker enhancements (from ue).
Eager should help in the first round too.
Probably using strongarm bracers for more dice isn't a bad idea either.

[Warlocknthewind]

I'm going to throw a curveball and say Ronin, from Complete Warrior. Full BAB, Sneak attack, and bonus feats that aren't too terrible. What makes this class great for such a build is Banzai Charge and Heedless Charge for an attack both surprising, and surprisingly effective.

Pump initiative, after your initial charge, people are going to be pretty aware of your location. Sneak attack by flanking, or charging, doing both is hard to do without HiPS, in a build already heavily invested. If you somehow have a spare feat, maybe pick up Cobalt Charge (or play an Azurin) to maybe dip three levels of Umbral Disciple after your two Robin levels? Shores up saves, skill bonuses, and sneak attack.
Edit: and HiPS

I enjoy the Scout/Ranger/Barb/Highland Stalker more for this sort of idea, because it doesn't rely on the awareness of the target, only on my ability to move, which can be difficult to limit if you're doing it right.

[goto124]

Just make your barbarian wear a special kind of make-up, and call him a Rouge Barbarian. Close enough.

[Optimator]

I bet some sort of Instant Rage/Intimidating Rage/Never Outnumbered/Imperious Command-based Barbarian/Rogue/Avenging Executioner would be functional. Maybe even squeeze five levels of Scarlet Corsair/Dread Pirate for faster Intimidating. A Swordsage dip with Craven on top...

I have a Rogue 3/Hexblade 3/Avenging Executioner ?/Ghost-Faced Killer ? who is pretty potent for his level. He's a (Necropolitan) zombie pirate so he can't get Craven but he gets a lot of bonus strength and the like from Corpse Crafter. Anyway, the point is I could easily see the Hexblade being replaced with some Barbarian.