Alright this is gonna hurt a little:
Attack of the Mutant Space Bats
Commander Keen (already listed, but it’s fun)
Clyde’s Adventure (surprised no one listed it yet)
Clyde’s Revenge (sequel to the above)
Asteroids (revisioned with semi-3d graphics)
Hugo’s House of Horrors I, II, III (no better text-walkabout game, not even Peasant’s Quest)
Jazz Jackrabbit (it’s DOS right? can’t believe i forgot this one)
Elfland (i love smacking birds out of the air with a flash berry)
Chex Quest (my first FPS, and quite possibly the only one i’m good at)
Mario 1, 2, 3 (obviously)
Donkey Kong Jr.
Final Fantasy 4, 6
Gundam Wing Endless Dual (yay, anime fighter!!)
G Gundam (yay, more of the same!)
DBZ 1, 2, 3 (ok, now that’s a bit much…)
MegamanX 1, 2 (still need to play 3)
Sonic 1, 2, 3, &Knuckles (totally awesome of course)
Streets of Rage
That’s all for now. Also, I refuse to believe that the Dreamcast is an “old” system, simply because it kicked so much ass, only it did it too prematurely, and no one realized that their asses were being kicked. I mean, seriously, almost-PS2 graphics during the PSone and N64 era? why did no one grab it? It’ll be old when the games become downloadable for the Wii.
Additionally, if anyone likes those old-timey DOS games, i’ve got a website for you: http://www.dosgames.com/
so cool. note that dos games are not emulators, but are free simply because they are really old. And the other games may be obtained through other means, whether legal or not, your choice.