The MBTI, or Myers-Briggs Type Indicator, is a typology created by Mmes Myers and Briggs, based on C.G. Jung's work.
I like it because it's free, it's quick to take, it tends to render very accurate results, and it doesn't tell you there's something wrong with you.
I encouraged many people to take the free anonymous evaluation° on the web, and the worst result was "A lot of this is correct!"... with the best being: "Wow, I've never been described this well, even by myself!"