I have been think of purchasing a Sega Genesis considering how cheap they are on Ebay

Can anyone recommend me some good games for it besides Sonic?

I also thought Streets of Rage 2 and Shinobi III were fun

Thanks!

Toe Jam & Earl
Earthworm Jim
Battletoads
Zombies Ate my Neighbors

Those came off the top of my head. I'm sure there's more.

Not sure what types of games you like but some of my favorites off the top of my head:

Streets 2 (which you already mentioned)
Phantasy Star 2
Ghouls 'n Ghosts
Thunder Force 3
MUSHA
The Revenge of Shinobi

EDIT: More excellent games that I forgot:

Castle of Illusion starring Mickey Mouse, Castlevania Bloodlines, Gunstar Heroes, Contra Hard Corps

Others that I thought were pretty good:  Mystic Defender, Aladdin, Golden Axe, Splatterhouse 3, Shining Force 2, Sword of Vermilion, Shinobi 3

Streets Of Rage 1-3
Comix Zone
Castlevania: Bloodlines
Contra: Hard Corps
Ristar
TMNT: The Hyperstone Heist
Aladdin
Earthworm Jim
Ghouls`n Ghosts
Robocop vs The Terminator
Gunstar Heroes
Golden Axe 1-2
Splatterhouse 3
The Punisher

Streets of Rage 2, Phantasy Star (any of them), After Burner, Altered Beast, Ecco The Dolphin, Kid Chameleon, OutRun, Road Rash, Super Monaco GP 2 and Moonwalker are some I remember right now.

Man, first one is a hidden gem, second is completely amazing (even the older SMS version is good) and the third is damn good classic beat n' up, he should definitively try these ones too.

Get shining force 1 and 2 and that is all you will ever need!

Vectorman, Earthworm Jim, Golden Axe, Ristar and Bloodlines are the Genesis games you must play!

Soleil, great lil rpg, even features Sonic as a Cameo.

If you can find it, and can't wait for the HD version to come out, get Pier Solar.