At least two Total War games and an Elder Scrolls game.
Originally Posted by Saluki
Mostly older games.
Gothic and Gothic 3, in case I want to jump in and run around for a while.
Test Drive Unlimited, my utitmate cathartic driving game.
Baldur's Gate and Alpha Centauri/Civ 2, on my laptop.
My last couple re-installs I've always downloaded Majesty 2 right away. Playing a mission every now and then is still pretty fun, and I haven't even touched 2 of the expansions yet.
Metro 2033. I always seem to playing a runthrough of this game.
I always keep X2 installed on my HD in hopes of restarting a game for real in order to finish the main quest, but I'm not so sure it will happen by now. Still - it's there.
Have you heard of the EasyTutu mod for Baldur's Gate 1? It basically takes that game and places it into the Baldur's Gate 2 engine. Makes it much prettier and more enjoyable. Huge number of bugfixes too.
Another thing you might be interested in is a mod called Planetfall, which is a brilliant remake of Alpha Centauri for Civ 4.