Hmm.
I like WoW's combat when it's done right. Though, WoW was kinda designed on combat on your own being rather boring, but combat as a group to be extremely synergistic and interesting. Plus it was more about "not standing in the fire" and position-dependent group work then having flashy ways to kill the other guy. So not really single-player material.
Dragon Age 2 would be my current nominee for best single-player RPG combat. (I haven't played Dark Souls or Kingdoms of Amalur so I don't know how well those fair, Amalur looks like it might be a contender if I ever get around to it.) There were some flaws (wave-based combat, some weak abilities, etc etc) but on the whole the ideas were great. Having easy access radial menus, all 4 face buttons on the controller mapped to abilities, every time you push a button something happened, no delays, misfires, constantly being bumped out of melee range before you could push the attack button or other problems.