With my interest in psychology and counseling, as well as in my quest to poke and prod places within myself, I often take the various online tests that I find (it is also why I like the meme, Unconscious Mutterings). Many are just fun and not to be taken seriously, though if they help you think about some aspect of self that you hadn't thought about previously, then they are useful. I have yet to see some reliability and validity results posted with these sorts of tests and as such, they should only be used as possible tools in the quest for self knowledge, if the results make sense to you.
One of the most interesting exercises to date is the visualization exercise known as The Cube. If you haven't tried it, go check it out. Be sure and take it without reading the answers of others and without peeking at the key. It is not a competition and there are no wrong answers; its value lies in your interpretation of your visualization using the key. I highly recommend it, so take a few minutes and try it. Don't cheat.
Visualization exercises fascinate me because they often help one get to layers that don't always bubble up to consciousness, tapping into a variety of subconscious things. I did post my answers there, and I might post my interpretation here later on. It did make me curious to read the book to find out what kinds of common themes people found. By the way, the author of the blog, AmbivaBlog, where the exercise is found, is also the author of the books I want to read about the exercise.
Another little test, I found recently through Don at Conscious Living Journal (whose poetry I have enjoyed for a while), is a more straightforward sort of question and answer that attempts to tell one the archetypes that are playing a role in your life. My answers to that one seemed to make sense to me, too.
The archetypes they use are some common ones, but there is no single set of archetypes universally accepted, rather there are 70 or more that are used in various ways by various different disciplines. For further exploration about archetypes, there is an interesting list found here.