I don't have much time right now, because I have to go pick up a play kitchen that's on sale at Toys R Us. I'll give you five for each:
PSOne:
Vagrant Story
Einhander
Castlevania: Symphony of the Night
Silhouette Mirage
Metal Gear Solid(Swap this out for Silent Hill if you've already played Twin Snakes)
Dreamcast:
Crazy Taxi
Marvel vs. Capcom 2
Jet Grind Radio
Armada
Sonic Adventure
Genesis:
Gunstar Heroes
Shadowrun
Sonic the Hedgehog 3
After Burner II
Comix Zone