Moustraveler revealed the shocking fact in the Mission: Space thread that Space Mountain doesn't bother him at all despite having motion sickness problems. Which rides bother/don't bother you?
For me, Expedition Everest is fine the first time and a bit upsetting after the second, but any more than that and I get nauseous. (It's the part where you go backwards that gets me) It's nice that I've had enough opportunities to ride it 3 times in a row to know this.
Space Mountain gets to me if my stomach is already upset, but otherwise is fine.
Mission: Space can sometimes give me a bit of nausea, but it goes away pretty quickly. I don't think I'd ever ride it twice in a row though.
Interestingly the Tea Cups, if I focus on the person across from me and don't close my eyes I can not only avoid nausea, but even dizziness!
RnRC can get to me a bit if I ride it multiple times.
Tower Of Terror I could ride all day without any ill effects.
It's A Small World usually makes me a bit nauseous after one trip, due to the repetitive music, and I shudder to think what riding twice would do!