Rogues get intimidate as a class skill (and paladins don't) and it's great mental image of a thief insulting some strong opponent running circles around them while dodging every attack and keeping their attention.
So rogues should totally have an intimidate prestige class to help them out. Fighters and Pallys get pres to help them and barbs can hate tank (rogues can't w/o radiance weapons)
While fighters and paladins use heavy armor and shields to block and reduce damage and barbarians have high hit points and inherent DR, I think the rogue pre should be based on a stinging bee. Won't really hurt you, is fast, unstoppable, and hard to hit... but can't take much damage.
I think the acrobat is a good base to start with since it models many of the aspects of this prestige class.
Acrobat I:
You gain +2 jump, tumble, swim, and balance and a 5% inherent bonus to run speed
You gain 2 extra uses of uncanny dodge
the dexterity bonus allowed by light armor is increased
You get a +3 shield bonus to AC when using a quarterstaff
+1 intim and AC
Acrobatic stance:
You gain a +2 dodge bonus to AC, +2 to saves, +2 dexterity and -2 constitution
Acrobat II
Your bonus to jump, tumble, swim and balance all improve by 2. You have a 10% inherent bonus to run speed
+2 uses of improved uncanny dodge
dexterity bonus allowed my light armor is increased
+5 shield bonus to AC when using a quarterstaff
+1 intim and AC
Immunity to most knockdown effects and slippery surfaces
Improved Acrobatic Stance:
You gain a +3 dodge bonus to AC, +3 to saves, +3 dexterity and -3 con
Acrobat III
another +2 to skills and 15% bonus to run
+2 uses of improved uncanny dodge
dexterity bonus allowed by light armor is increased
+7 shield bonus to AC when using a quarterstaff
+1 intim and AC
You treat medium armor as light armor
Greater acrobatic stance
You gain a +4 dodge bonus to AC, +4 to saves, +4 dexterity, -4 con
You move as if you had perpetual freedom of movement
So that's my rogue "tank" that is based on the idea of a constantly moving rogue that is hard to hit or stop
And I also came up with some idea for a barbarian prestige class based on an unstoppable juggernaut. While the other tank classes try to avoid damage, he shrugs it off and keeps going.
Juggernaut I
You are an unstoppable force, it is easy to hit you, but you are hard to hurt
+1 intim, -2 ac, +4 to barbarian DR
Barbarian movement bonus increased to 15%
You gain light fortification
+30 hp
Juggernaut Rush
While in this stance you gain +2 con and +2 saves but your ac is lowered by one
Juggernaut II
+1 intim, -1 AC, +2 to barbarian DR
Movement bonus increased to 20%
moderate fortification
another +30 hp
Every time you are hit, there is a 10% chance you gain 20 temporary hit points that last for one minute
Improved Rush
+3 con, +3 saves, -2 AC
Juggernaut III
+1 intim, -1 AC, +2 to barbarian DR
movement bonus of 25%
heavy fort
+30 hp
Improved evasion
Greater Rush
+4, +4 saves, -3 AC
so just some ideas I had of cool intimidate prestige classes for both
I think they both need some tweaking, but I'd like to see something for this for them sometime
Shield blocking for 20 minutes isn't the most run raid experience which is probably why there are so few tanks. I think this would help get more toons out there who can tank Harry and Sally and Xzyzzy which means shorter raid loading times for everyone