Since we're in Minecraft limbo right now and I have about a million games I've been putting off:
Painkiller Black Edition. Since I had to install Windows 7 on my Mac (via Parallels) for a project I thought I'd try a couple of games out that I used to run through Crossover but got fucked up (wouldn't run for whatever reason) half-way into the game.
So far, so good. I may even install Steam and pick up a small title just to see how it goes.