Xbox offers a higher variety of blockbuster action/adventure games--Modern Warfare 2, Wet, Halo...etc. However, it is made more cheaply than Playstation. There have definitely been more reports of the Xbox going fry-o.
Playstation is going to have more in-depth, story driven games, as I see. Metal Gear Solid 4 (AWESOME!), Heavy Rain, and the like.
If you are looking for superb FPSs, definitely go with the Xbox. Playstation is very pricey, anyway.