Committee for the Scientific Investigation of Claims of the Paranormal
http://iquest.com/~fitz/csicop/resources/skeptical.html
If you doubt the claims of paranormal activity, magic, UFOs, creationism, and things that go bump in the night, this is the site for you. This site has links to various skeptic groups around the country, such as the James Randi Educational Foundation, and magazines such as the Skeptical Inquirer. It also links to a site taking apart the "Alien Autopsy" film.