• Sheldon Brown’s Bicycle Technical Info
  One of the most comprehensive cycling sites on the web. This site is particularly useful for fixed wheel converters.
• eHow Bicycle riding and maintenance
  A collection of instructional articles and videos
• Bicycle Tutor
  Lots of how-to and diy repair videos
• Park Tool repair help
  An extensive blog with repair articles. Also, each tool on the Park Tool web site has its own instruction manual!
• Bike collective network shop manual
  A wiki with a number of repair articles, from beginner to advanced.

(more coming soon, hopefully)