If you have never taken one before, I recommend starting with the Myers-Briggs.
Over the course of my life I have had occasion to be around people who saw no value in an assessment a personality test could provide. There are certain types of personalities who actually hate taking a personality test (which you should know makes shrinky types like myself a little suspicious). So why are they useful? I mean, don't we pretty much already know ourselves? Isn't it kind of like reading a horoscope and then just agreeing with all the things you want to see in yourself? No. Not really.
The point of a personality assessment is to figure out where your strengths and weaknesses are. They can be helpful when interacting with others, and they can be helpful to get to know yourself better. They are one way to help determine career paths that would be a good fit and career paths which might not. Obviously people are complex. A personality test is not an end all be all that would describe a person. There are many variables that make us who we are and a personality test is just a tiny measure of some specific aspects of how we interact with and experience the world.
The Myers Briggs is based on the archetypes developed by Jung. Sometimes the Myers Briggs is dumbed down into some of the "color" theories of personality. Those are a broad way to look at a much more complex topic. The color theories usually present 4 main "world views" - typically blue, gold, green or orange. Sometimes those measures are easy to see in people. You can kind of get a vibe of where people might fit in those categories fairly easily. But the Myers Briggs actually breaks that down into 16 specific types.
Here's a pretty good online version of the test (the real test is longer, but this is still a pretty good device): Myers-Briggs short test
I've known my type (INFP) for a long time. It's probably a big part of why I've always wanted to go into counseling.
This is also a pretty interesting test: LifestyleQ's
This breaks people down according to theories developed by Alfred Adler (possibly the 3rd most influential person in the field of psychology behind Freud and Jung).
I feel like this is the most boring blog post ever! But what would really be interesting is if people I knew commented with their Myers-Briggs determination.
But maybe that's only fun for people who dig psychology. ;)