This guide provides links to (mostly) free resources online to find information about individuals including names and aliases, birth dates, addresses, criminal history, and employment.
This site is maintained by the author of "The Investigator's Little Black Book." The site is particularly robust, with many good starting points, especially when researching outside of your home state.
California private investigator Tamara Thompson maintains pibuzz.com. It has links to hundreds of different investigative websites, as well as useful tips and tricks.