Conquests of Camelot, especially because it was the very first computer game I ever beat all by myself without my parents or older siblings helping me. Conquests of the Longbow, too, because I have loved anything to do with Robin Hood stories since I was very young.
All of the King's Quests, but especially I and V. I also have many fond memories of playing Quest for Glory IV (and all of the games in that series, really).
The one that takes the cake as far as nostalgia and fond memories go is Phantasmagoria, though. Hee. I have more in-jokes about that game than anything else in the world.
