I wasn't a Sega fan back in the day but I recently picked up a Dreamcast and Genesis for $15 each. However, I'm lacking in the game department. All I have for my Dreamcast is Soul Calibur and Resident Evil Code: Veronica and all I have for my Genesis is Mortal Kombat and Sonic the Hedgehog 2.

So, can someone name some good games for both systems?

Edit: Playstation games aswell. xD I only have FF7 and Parasite Eve. >>; This is what I get for only going Nintendo until now. xP

Any Sonic games ruled back then.

Genesis:
Lion King
Toy Story
Castle Of Illusion: Staring Mickey Mouse
Zero: The Kamikaze Squirrel
Rocket Knight Adventures
Gunstar Heroes
Madden 1990
NHL Hockey 1990
Road Rash
Garfield: Caught In The Act
Bubsy 1

Dreamcast:
NHL 2K
NFL 2K
Crazy Taxi
Airforce Delta
Starlancer
Sega GT
World Seies Baseball 2K2
Flag To Flag
The Grinch (weird I Know, but it was good)

Get Sonic 3 and Strider for Genesis. I personally love the Sonic Adventure-games for DC too, but some people don't. Also try and pick up Shenmue 1 & 2.

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

I do not agree with that assessment. Sonic 3D Blast did not "rule." 

Genesis-Streets of Rage 2, Sonic 3, and Vectorman.

Dreamcast-Sonic Adventure and Jet Grind Radio.

Playstation-I did not play the PS as much as other systems, but Resident Evil 2 is a magnificent game.

Herzog Zwei. I recently picked up a copy myself :)

Dreamcast games to consider:

Powerstone 1 & II
Skies of Arcadia / Eternal Arcadia
Jet set radio/ Jet grind radio
Daytona USA 2001
Crazy Taxi
Street Fighter III third strike
Marvel Vs Capcom 2
Shenmue
Ferarri F355
Outtrigger

Maken X

Rival Schools Project Justice

Changed Onyxmeth's list to add some of my own. Mine are in bold

Genesis:

Aladdin
Earthworm Jim
Phantasy Star IV ( Currently playing on Wii. Fantastic ! )
Gunstar Heroes
Tunderforce IV
Street of Rage 2
Shinobi Revenge
Sonic 2
Shining Force 1/2
Warsong
Musha Aleste

I just found out that my mother got me Metal Gear Solid and Final Fantasy: Origins for Playstation for Christmas. xD

But yeah. Thanks everyone! I have Sonic Adventure 2 Battle for GCN but I've always wanted the first one. I'll look into that. And I think I'm gonna get Resident Evil 2 for GCN.

Other then that, I'll look into the games you all posted. Thanks :D