here are two websites where your can take the Myers-Briggs Type Indicator Test:
and you can decipher your type here at Typelogic.com (as well as on the websites themselves).
there are apparently 16 types of personalities in the world, each having four aspects to it. you can find out more about the test here.
i'm an INTP, although i took a more comprehensive test from this book i got a couple years back from Barnes & Nobles.
aaaaand Testcafe.com does free Enneagram Tests as well. it is similar to the MBTI, but there are only 9 different types in this test. i'm a number 5.