My ongoing heads up battle against Sparbot, the Univ. of Alberta poker model
Though it doesn't happen very often in a cash games, heads up poker (just you and one opponent) is the gauntlet you have to master to win any poker tournament. It's actually a good exercise for the rest of your poker career as well. Most of what you do in poker is learn about what range of hands to play in this situation vs. that one, as well as how to put your opponent on ranges of hands.
Those ranges are incredibly wide when playing heads up, and once you really get a good feel for heads up play, you move around in that range quite comfortably since you've seen one end of the scale. Having an understanding that playing Jack-Six is ok heads up, though it's junk at a full ring, and even understanding HOW you should play it is a valuable skill.
So one of the drills my coach has me do is play heads up against Sparbot, from the Poker Academy training software from the University of Alberta's Computer Science Poker Research Group. Sparbot is an algorithm that attempts to play a game-theory perfect implementation of poker. When he raises before the flop, he could have Jack high or Ace-Ace. The algorithm works hard to balance its actions so you never really know what he has. There's no intelligence in there to exploit your weaknesses, so this should be the "easiest" bot to beat.
I've taken to playing 300 hands sessions of Limit Texas Hold'em against Sparbot and keeping track of the data (of course). I do appear to be getting better as you can see by this graph below, but I haven't shown consistent wins yet.
This graph shows how many small blinds per hand I won against SparBot for my roughly 300 hand sessions. As you can see, it still wins money off me, but it's been getting less and less over time.
You're also going to want to play heads up against a real human. I can't put my finger on it, but they definitely feel different to play against. Sort of a "poker Turing Test", I suppose. If you're going to play live, you really want to start with a list of poker sites and check out both the rake and whether they offer heads up tables. I've played a lot of heads up on PokerStars, so if you choose that site, you'll have plenty of opportunities, starting with $.25/$.50 limit, to battle it out mano a mano.