sudoku.com: Sudoku by Pappocom -- the home site for everything Sudoku, including the Sudoku computer program, and home of the Sudoku Players forums.
Sudoku Online: Sudoku tips, strategies, information and help from Michael Mepham for London Daily Telegraph and Los Angeles Times solvers.
Wikipedia: Sudoku information in the Wikipedia.
Web Sudoku: Billions of Free Sudoku Puzzles to Play Online.
Sudoku Fun: Online Su Doku Puzzle Speed Challenge.
Sudoku Puzzles: Free Sudoku Puzzles. Play online for free.
Sudoku Links: A lot of sudoku links list from Holland.
Sudoku League: How quick are you?