Help me buy a futon

[Jack of Arcades]

So I want a futon 'cause my bedroom is sorely lacking a couch. I have no idea what to look for, though. I want to spend < $500, and hopefully it'd fold out into a full-size bed. If the frame's uncomfortable I don't really care, as long as the mattress is pretty good; then I could just toss it onto the floor and sleep on it.

Who else is a college kid and knows where to find a decently comfortable, decently cheap futon?