Most FPS make me ill. Descent did it for me as well. I seem to be fine with COD4MW2 though. Eternal Ring was another that made me sick. Even the original Morrowind would make me a bit queasy after an hour or so. Descent took about 10 minutes to make me feel sick.

But here's the part that I find odd. I don't get motion sick in actual events. Sailing, motorboats, helicopters, planes (even small planes in turbulence), cars, hot air balloons, anything. I've only once had any adverse effect from motion. After spending two days about a small watercraft in fairly rough seas, I felt like the ground was moving and was a bit dizzy for half a day once I got back to land.