Site with puzzles compiled by Norwegian Vegard Hanssen (Don't worry the site is in excellent English by the way) with 6895702 puzzles at the time of listing with more added regularly. There are also 569829 Wordoku puzzles and a two person Sudoku game called Sudokuto invented by Hanssen.
Printsudoku.com Daily Sudokus in PDF form to print out, with an archive of previous puzzles.
The Daily Sudoku
This site features a new printable Sudoku puzzles every day and has an archive of over 150 puzzes which are also available to print off. You can also ask for a hint and check the solution. An e-book of puzzles is also available. The site also include a sudoku forum so that you can chat to your fellow addicts.
Sudoku Quotes and Tips The only skill involved in sudoku is logical deduction. Cryptic crosswords require a fair amount of cultural knowledge; sudoku is cross-cultural. Dr Anuj Dawar - Cambridge University