Deus Ex,Dead Space 2

Assassin's Creed II. Best game in the series IMO.

Deus Ex - 10/10 - Must play
Darksiders- 7/10 - Play
Hitman: Blood Money - 8/10 - Play
Max Payne - 10/10 - Must play
Trine- 10/10 (if you like platformers) - Must play

Hard to go wrong with Mass Effect

Team Fortress 2.

payday, AC2

Darksiders maybe.

Looks like you've already decided on Mass Effect, but for future reference, The Backloggery is a great site for managing your backlog, and you can even ask it to pick a game for you. It's also just a great way to keep track of all your games if you're weird like me and want to do that. :D