From what I've heard, the Myers-Briggs test is fairly accurate, but even the paid MBTI evangelists say that reading through detailed descriptions of the various types to find the one which feels most familiar is better. The detailed description part is important, because the details (about a page per type, IIRC) go into both the strong and weak points, providing pressure to reject descriptions which have flaws that feel inaccurate.

From what I remember, the corporate paid evangelist visits generally do type testing three ways: Written test, description-based given by your peers, and description-based self-report. The first is for calibration, the third is the main assigner, and the second is basically a conversation-starter; the idea is to discuss ways in which people feel different internally from how they're perceived.