J.T. O'Donnell from Career Insights offers her online ISAT (Interaction Style Assessment Test) for free.
I love tests that take less than 10 minutes to complete and with explanations that can be understood without using a dictionary.
Don't forget to mention your interaction style in the comments!
Me, I'm a Contemplator. Although I don't like that one of the typical areas for a Contemplator is Accounting, I can't really argue with the results ;-)