In no particular order...
No More Heroes
No More Heroes is really not that good of a game, but guess what,
No More Heroes doesn't give a sh*t. And
No More Heroes wants you to know it doesn't give a sh*t. Proving that you don't need substance as long as you have attitude,
No More Heroes is one of the funniest most balls out games I've ever played, so much unlike anything else that even if you expect it to be crazy it will leave you staring at the screen asking yourself "what did I just see?".
Audiosurf
At its worse,
Audiosurf is an addicting puzzle/action game with a soundtrack of your choosing, at it's best it's the perfect merging of music, visuals and gameplay. Considering how much I've spent playing this game and how much fun it still is, I kind of had to put it up there.
Baldur's Gate 2: Shadows of Amn
Hands down the best RPG I've played. Great story, memorable characters, well written dialog and gameplay deep enough to provide a different experience every time you play the game.
TimeSplitters 2
If there was ever a perfect split screen game, this is it. Whether it's the co-op campaign that spans 10 barely connected missions in different time periods or the split screen
Goldeneye-style vs mode with,
TimeSplitters 2 is the quintessential couch shooter. Also, monkeys. Loads and loads of monkeys.
SSX Tricky
Why just race or just preform fancy tricks when you can do both at the same time? Throw in some Run DMC and a ginger with an afro and there you go: the recipe for fun