Enjoy your PS3! I'd personally try to hang on to the Xbox, just because it's always easier to store it and play a few games now and then as needed. If you do sell it, remember you can always get a cheaper and more reliable 360 later on down the road. (I think they're beginning to fix the quality problems, but it will take time).
Haven't had much time for play-throughs, but I can personally vouch for "Ratchet and Clank" and "Resistance" - both hugely fun titles, worth every penny.
Finally, if you have a quality HDTV (1080i or 1080p), be sure to get the most out of the PS3's BluRay playback. I didn't think BluRay mattered that much when I first got my 60GB PS3 , but then one night, on a whim, I popped in a Bluray release of "The Road Warrior" and the visuals knocked my socks off. My jaw hit the floor so hard, I think I damaged some fillings.