Most people I know, myself included, have games from their past that they remember fondly. Unfortunately, most attempts to revisit this ancient fun are met with disappointing results as we realize that not everything that was fun back then is fun to us now.
The good side of this is that you sometimes come across a game from your past that is simply timeless.
I keep thinking I'll put up some new blender material or maybe some programming goodies, but I've been lacking the time and the clarity to get any of it done. (Maybe these old games have something to do with that?) Instead I'm posting some older games that remain awesome.
The Ur-Quan Masters
Mechwarrior 4 : Mercenaries -- Online play doesn't work through MS anymore, but there are community mods.
http://www.mektek.net/ -- Community site
This list could get long so I'll stop there for now.