Via Nag on the Lake, take the MENSA workout test here.
After submitting my answers, I was informed that I "would have a good chance of passing the Mensa test". Thanks, but I think I'll pass on taking a test to join MENSA given that its statement of purpose is "to create a society that is non-political and free from all racial or religious distinctions." In a world without politics, I'd be unemployed and awfully bored.
Besides, joining an "international high-IQ society" looks like an expensive proposition.