Less graphical entrance:
Robert T. Carroll, a philosophy professor at Sacramento City College, provides this site, with a credo that says "the only thing infinite is our capacity for self-deception."
It is highlighted by 250 skeptical definitions (in the form of short essays) on topics from acupuncture to alien abduction to zombies. Definitions are hyperlinked to related articles, and sources for further reading are also provided.
For those who lack the time to savor the dictionary, the FAQ (which begins by questioning if skeptics can be skeptical of skepticism) gives a wonderful flavor for the site.
Note: the dictionary is also available in Portuguese.