The latest tank in my group was actually a scout/ fighter combination. He specialized in making AoO's, and his feats looked something like this: Combat Reflexes, Combat Expertise, Improved Trip, Hold the Line, Karmic Strike, Dodge, Mobility, Spring Attack, and more.
He would attack with either Spring Attack, or use his monstrous tumble check to move through threatened areas and attack, which qualified him for his Skirmish ability.
The rest of his attacks in a round were AoO's and all benefited from the Skirmish damage. When an enemy tried to move next to him, they were hit with a +12 or something trip attempt AoO, followed by the free attack. Anyone that got through met another AoO from Karmic Strike if they managed to score a hit. It didn't help that he had something like 8 AoO's per round, and an AC in the lower 30's.
How did I deal with him? Ranged missiles worked well, though only for a short time because he could quickly close distance. Spells worked nicely, but he had evasion and a high dex so reflex saves were worthless. Anything with larger reach tore him apart. Grapple was out of the question due to close-quarters combat. But I did find that his attack bonus wasn't that great, and when he ran into the BBEG with his +4 Full plate and +5 tower shield it was lethal.
I've also had a halfling monster in an epic game. He rode a winter wolf, had levels in Paladin/ Cavalier/ Halfling Outrider, and could charge for something like 500+ damage. Unfortunately, this holds true for most mounts, it's rare when they're as powerful as the PCs themselves. Killing the mount was an easy matter, as was incapacitating it (Hold Monster, Flesh to Stone, Baleful Polymorph). Also it's nice to note that charge can't be used in hindering terrain, or against opponents that have cover, and can only be used in a straight line. Plus, there are two spells that abosutely kill a charging character, Waves of Exhaustion and Waves of Fatigue. Both spells have no save and take away you're charging ability, and require hours of rest to get rid of.