Bridge Guys A comprehensive collection of information about conventions.
Richard Pavlicek. His monthly contests are difficult but excellent.
Bridgebum (Jeff Tang) The "Food Asking Bids" are my idea of fun. Also in his excellent collection of articles is a reprint of the Grosvenor Gambit article from BridgeWorld.
Carl's Lessons Different. Half of the website is devoted to opening 4-card majors.