Rainbow Six Vegas is great single and multiplayer game...*****
The Elder Scrolls IV: Oblivion
Those are My top two game.
Ghost recon 2 is good but short( finish first one)
Driving:
Burnout 3 or Project Gotham racing or Forza 2
Gears is great online and co-op is awsome for when you get live.
Plus single player is fun
There is Guitar Hero, but not every ones game.
Hope this helps
Just picked up my 360 premnium one. I got Lost Planet, Ghost Recon(the first one), Halo, and pre-ordered Halo 3. I know Gears of War is an awesome game, but I'm looking for something with a little longer single player, as it'll be awhile before I get the wireless adapter for Xbox Live. Going to get Halo 2 soon, after I beat Halo. Any advice welcome!!
treemen

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic