Sometimes I'll boot up my PS2 emulator and play War of the Monsters: My god it's so awesome! EDIT: Oops I mentioned this game twice. That's how awesome it is.
WZ2100. I downloaded the latest patch last night. In the past fifteen years, a small open source community re-did the textures, the AI, and the render path. But they still kept that fantastic atmosphere. Oh, unit models have less polygons than units in PA!
Ever tried Hacker Evolution? It's like Uplink and currently on sale: http://www.bundlestars.com/all-bundles/the-hacker-bundle/
So uh, how about the GBA pokemon? Or Super Smash Brothers Brawl/Melee (I play both, depending on the emulator and boredom). OH! I play Civilization II: Test of Time. Love that game. Love it.
My high school has actually picked up a tradition of playing an Adobe Flash port of Super Smash Bros Melee (called Super Smash Flash) during exam week on the school computers. We plug in our USB cables and disconnect the Ethernet cables and have 4 people playing on the same keyboard. It is STUPID fun and reminds me of the good old days of gamecube. Always hated Pokemon though. Never understood why people liked it.
We had a night at the bar near the university where they hooked up an N64 to the TV and we played Mario Kart / Party and Goldeneye. Goldeneye has NOT aged well...