BASE jumping both terrifies and fascinates me to no end. As a general rule I don't mind heights, I don't get motion sickness, and I can play vertical-heavy games like Jumping Flash and AaAaAA!!! - A Reckless Disregard for Gravity all day long. It's just the falling part that really freaks me out.
Naturally, I had to try out Skydive: Proximity Flight, and was pretty surprised with the results.