In the DOS/Win98 machine:
Star Wars Jedi Knight: Dark Forces II
In the Windows XP machine:
SimCity 4 with Rush Hour
Diablo II
Supreme Commander: Forged Alliance
In the Atari 5200:
Pac-Man
In the Nintendo:
Nothing
In the Saturn:
Tetris Plus
In the Playstation2:
Madden '05?
For Diablo II I play with a mounted rip so it's only virtually loaded. Lately I've been playing some hardcore ladder on B.net East and I hate swapping discs, plus there's less load time with ISOs in the game between acts and with voices/animations.
I'm not sure what Madden game is on the PS2 at the moment because my brother switches between it and some racing game. Whenever I'm down there, lately I've been playing Taito Legends 1 & 2.