Stunt Car Racer Turbo (faster than original, linkup, can't go wrong and more you have players better it gets.. 8 players league is super entertaining always)
Super Skidmarks (linked up, split the screen for each computer to get whole track visible at once, 8 players with 4-player joystick adapters... can't get any better)
Lotus2 (linkup, 4 players.. seems to work)
HBMonopoly (max 8 players on network play, just damn working monopoly game.. countless hours and nights wasted with this
dynAMIte (massive Dynablaster clone with network play, oh those hectic nights betatesting this.. seems to be quiet nowadays to get random players with, but if you gather some friends, still fun)
WormsDC (4 players, damn fun always)
Nitro (3 players, fun racing)
Masterblaster (for more simple dynablaster style game, 5 players)
Blitz Bombers (max 16 players split machine fully boosted fun)
SWOS (more the players in the league more the fun)
And then some two player favourites:
Napalm (just perfect RTS fun with linkup, no other RTS game has this balance on two player game)
Super Cars 2
Settlers
Turboraketti
Pro Tennis Tour 2 (actually 4 players could play this, but I've never tried.. should try)
Co-ops:
Rodland
SWIV
Well.. there are so many others too, but my mind is getting empty just now... I guess those are the most played games here anyway.
Knights of the Sky felt the best flying simulator for two players in old times.. haven't tried those lately though.