No specific order:
Starcraft: All of them. They are just amazing.
TF2: Most balanced and well thought out shooter ever.
Minecraft: Well more specifically Minecraft Tekkit but even normal Minecraft is AMAZING. Just need tekkit to be updated to MC 1.3 and it'll be even more amazing
World of Tanks: Best F2P game...ever...
Torchlight series: TL1 is certainly a worthy successor to Diablo 2. Heck it was made by the D2 team anyway. TL2 comes out in 3 days and I'm excited :D
Halo franchise, I'm Halo'd out admittedly, but it was part of my childhood and I still look forward to Halo 4
Mass Effect Series: ME3's ending sucked but the series was still sick
Lost Planet Series: I await LP3 patiently. The series thus far has been pretty damn good I must say.
CoD4: The last Call of Duty game to get Multiplayer over 90% completely balanced. Every one after is just an imba piece of crap. True WaW and Black Ops have Zombies which is fun but still
Battlefield 3: Amazing Shooter, way better than any CoD game
Blacklight Retribution: Also amazing shooter better than any CoD game. Plus, its F2P :P