A good test consisting of 70 questions for each of which you have to choose one of two responses. The tests uses the Myers-Briggs theory of sixteen types, when you find out which type you are you can see a description of your personality. This test is used with the kind permission of David Keirsey who runs the official Keirsey website . The results of this test are logged for ongoing academic studies into the nature of personality on the internet. In The Mood offers a variety of profiles that are research based and are very specific including a version of the Myers Briggs Personality Profile.
All tests are free and have in-depth information accessible.
Monster Trak A site with a lot of good articles about working and job searches. Also has a job profile section where you can find out real information about a field you are contemplating. Begin at the bottom and work up. A site mostly focused on the student entering college, but with a fair amount of career and after college based materials.