The following self assessment sites are free of charge and are a good substitute for more formal interest inventories. You may want to discuss the results of your interest inventory with a guidance counselor, teacher or other adult.
The Career Interests Game
Developed by the University of Missouri Career Center, this "game" is based on John Hollandís theory and resembles the Party Exercise by Richard N. Bolles. Each Holland type has links to job descriptions, education and training, employment outlook, and salaries from the Occupational Outlook Handbook. Click on "Career Interests Game" under "Quick Links" at the bottom of the page.
The Keirsey Temperament Sorter II
The Keirsey Temperament Sorter is a fun, interesting, and revealing questionnaire that identifies a Rational, Idealist, Artisan, or Guardian temperament. It will also suggest appropriate careers. This 70-question assessment is related to the Myers-Briggs Type Indicator. To use, click on the "Take the Keirsey Sorter" button. The temperament description is free, but there is a charge for the 10-page Character Report and the new Career Report.