The Longest Journey for $10 - albeit old, definitely one of (if not the) best adventure games of all time. Also X-Com: Terror From The Deep for $2.45. Apparently it runs on XP, too. Nice.

Deus Ex: Game of the Year edition and Deus Ex: Invisible War for $24.95

I've experienced some crashing issues with Deus Ex: GOTY. Your mileage may vary.

Deus Ex GOTY works fine for me. (It even works well through Wine)

One thing I've noticed is that on a fast computer (dual core with a really good vid card) , DE:GOTY seems to run too fast in regards to gameplay (npcs move about 2x as fast as they should and as such the game is almost impossible without cheats)

I have Game of the Year edition, runs fine. It's a CD version, though. But then, I've a 1.4 processor, so I don't think that counts for a very fast computer, heh.

page, if you are running on a dual core you need the processor driver. that kinda thing happens in a lot of games because of the dual core. you can also alt-tab out of the game, ctrlaltdel, go to the process, and set affinity so it only runs on the first core.

If they have X-Com running on XP, do they have Master of Magic on XP?