My top 3 (for what it's worth, which is possibly not a lot
)
Stunt Car Racer - top game! If you haven't tried it yet - stop reading this and go and play it linked up!
Populous II - feel my firey volcano wrath, evil-doers. Oh, the fun you can have plonking a massive volcano in the other persons main towny area.
Powermonger - Roast mutton anyone? (meeh) Splatter your friends with catapults and wait for the screaming as their army is annihilated with maximum prejudice!