This site provides an excellent catalog of logical fallacies and how they are commonly used to obscure the truth. It provides a great foundation for anyone interested in using the tools of logic and reason to advance or discredit a particular point of view. (Thanks to David Rood for recommending this link.)
Frank Visser's page dedicated to all things related to Ken Wilber. Ken Wilber is thought of by many, including myself, as the most comprehensive and insightful philosopher of our era.
Site dedicated to Robert Pirsig's philosophical theses expounded in Zen and the Art of Motorcycle Maintenance and Lila. The site also contains many links to other philosophical discussion forums.