Here's a list of the "well-reviewed" PS3 games. Go through, find ones you can't play on 360, and see for yourself whether you'd like them or not.
As a blu-ray player, PS3 cannot be beat. Easy and constant internet connections means you're always up-to-date on your firmware. May not seem that important, but Sony has plans that would allow any existing blu-ray player to handle 35 GB discs (instead of the current 25gb) with a simple firmware upgrade.
Also worth mentioning - upgrading to a higher capacity hard drive is much cheaper than on 360, since you don't have to buy an official Sony-branded HD.
That should give you a start, but you should really do your own homework. Buy a Ps3 because you want one, not because some random internet guy convinced you to.