Mmh. Most games i like to play have already been mentioned.
If graphics aren't your main concern, I would check out the underdog site
www.the-underdogs.org.
They have tons really good classics. If you like rpg's try Wasteland, which has still a very loyal following even though it's from 1987.
On a side note: I really enjoy EU II and Victoria, the community is pretty good , too. My recomendation: get'em play'em. The money is not wasted.