To second Elcs, Descent 3 was bad. To date, still the only game made me feel BADLY nauseous.
Oddly, watching my brother play half-life 1 would make me slightly motionsick, but I could play the mods all day long no problem.
Half-life 2, I don't know if it was just a bad day, or if the game also made me slightly nauseous.
Googling....