After some good times with Sims 2 and Civ III I'm back to my alltime favourite game, and expanding Lady Dierdre's Green Gaian faction across the face of Alpha Centauri.
A few days ago I found a great website for desktops that expand the mood of the game outward. It's fun because I sort of feel like I'm actually in space, on that other world.
If you like rendered spacescapes and moonscapes, check out Moodflow. Makes a nice change from Bondi Lines.