From: Little England
Alpha Centauri is the main one, I actually play that quite a lot, even today. Last played it a couple of days ago. "Chairman Banana, your police state is godless and wretched!". I think it has aged well, I prefer it to Civ4.
I actually play a lot of old stuff, not been all that interested in new games for a while. I bought Aliens vs Predator the other day, but it sucked IMHO. It did, however, make me install the ten year old Monolith game, AVP2, and that was much better.