Dead or Alive 3 is a good fighting game, as is Soul Caliber 2.
Halo is a great FPS with a good story to boot. Worth the 30 bucks it costs now.
Splinter Cell is a hardcore stealth game, so if that's your thing (and since you got Metal Gear Solid 2, I'm guessing it is) give it a go. Pandora Tomorrow also looks good, though I haven't played it.
FUsion Frenzy is good if your into Mario Party-esque games.

There are many others, but these are the only ones I've played I liked. And to think, I doion't even own an Xbox. I just play my friends.