My honest reply is buy a PS2 now and wait until something really cool for the PS3 comes out to buy it. (FF XIII or DMC4, maybe.) The PS2 is the same cost as two PS3 games, so if you spend more time with it than you would with those two games, you'll come out ahead.
If you choose not to follow my advice, go and find a list of upcoming games for the PS3 and start reading it. For all the titles that you're interested in, ask yourself, "Is this a game I can play on some other system that I own?" and "If so, is playing it on the 3 worth the extra $10-$20 that I'll be paying for it?" If there's a bunch of titles coming out that you can only play on the PS3 (and the only real exclusive that I saw was MGS4, and that's not out until September at the earliest), then buy it. Otherwise, wait until there's stuff on the PS3 that you're wanting to play.
Plus, the longer you wait to buy the PS3, the more refined the technology becomes, and the fewer possible problems that you'll have with it. And the longer you wait, the more of a chance that Sony will discount the price. Or bundle in a better title that Tallegeda Nights for a movie. (Although I think it's Casino Royale right now. If you wait until fall, it'll probably be Spiderman 3.)