I bought Galactic Civilizations 3, a game whose imminent release was enough in and of itself to get me to install a Windows partition. 4X strategy in space is a genre of game that I go way back with, and I'm looking forward to sinking a ton of time into this.
Another space-based PC game I'm looking forward to is Elite: Dangerous, which launches for Mac in a week. To prepare for that, I've spent too much money on a Thrustmaster T-Flight Hotas X Flight Stick to play it with.