Something like x-com or a really good turn-based strategy game that two players could battle it out (virtual warhammer 40k or soething like it) with downloadable squadrons and such! archon was great but a little dated for todays gamer, but something in that vein wouldn't be too bad...
Golden Axe 1 &2
The original Arcade version of Ninja Gaiden
River City Ransom with online play
Double Dragon 1, 2, 3 with coop online
Heavy Barrel With coop online
all of the D&D arcade games (3 if I remember correctly)
Mike Tysons Punchout (any version though the super version ould be great!)
X-men arcade game
Powerstone
Dark Stalkers
Rival Schools
P.O.W. (obviously with online coop)
Duke Nukem 3D
Space Harrier (preferably the newer 3d version)
I can think of more, but this should be a good start...
Live GT:Bool Zero
PSN: BoolZero
Wii NO#: 1482 7710 3479 1804