I'm constantly looking for games to scratch specific itches, and am in need of some new ideas.  I'm going to throw out some genres and games that I consider to be the best current option for time spent.  Feel free to nominate any games you wish and add new categories.  The idea isn't to nitpick over what the best option is, but to throw out some ideas as to what people should really be spending their time on.

Competitive RTS
Demigod
League of Legends

Co-Op RTS
Dawn of War 2 

Co-Op FPS
Left 4 Dead 2
Borderlands

Competitive Team FPS
Call of Duty Modern Warfare/2
Team Fortress 2 

Single Player FPS
  Fallout 3

Single Player Action RPG
Torchlight 

MultiPlayer Action RPG
Diablo 2
Titan's Quest 

Single Player RPG
Dragon Age

City Builder
Tropico 3

Casual
Plants Vs. Zombies