I dont know about the other people in this thread, but the only thing that really gives me trouble in a 1v1 are mages druids and the occasional paladin other than that I have a very balanced fight 1v1 with the other classes.
For all the tips below Hamstring should be up 100%
Rogues: Keep Rend up, if they use evasion, you win.
Hunter: Use normal abilities, if he feigns death gain some distance, he likely laid a freezing trap.
Warrior: Comes down to who is the better warrior, be sure to use Berserker Rage if he fears, and try to stance dance to disarm him, he will do the same.
Shaman: Dunno Im horde so
Priest: Similar to Warrior, berserk if they fear, pummel when they try to heal, use MS liberally.
Warlock: Berserker Rage, Hamstring, pummel if he tries to fear again, watch out of succy, Skull of Impending Doom helps here.
Mage: Pain in the ass, Frost Nova should be trinketed, intercept him, get in some more hits, you should be able to catch him if he stays around to cast at you, his hp will disappear when you do.
Druid: Annoying, a good druid will root and shapeshift out of hamstring, just keep applying it so he uses up his mana from shifting all the time.
Pally: Can be a pain, the only other high armor class. Keep up rend, watch for hammer of justice, if he consecrates try to kite him out of it, smart ones will take the chance to heal, so intercept into them to stop it. If he bubbles, its a good sign, take the chance to bandage while he heals, and take him out.