Sudoku

Asymmetrical Sudoku
Includes a generator and solver.
http://sudoku.netgubbi.dk/

Bob Hanson's Sudoku Assistant
JavaScript-based gameboard and solver. Can use cross-hatch scanning and subset elimination.
http://www.stolaf.edu/people/hansonr/sudoku/

BrainBashers
Offers daily puzzle in one of three difficulty levels. Archive of daily puzzles and an assistant.
http://www.brainbashers.com/sudoku.asp

Braingle Sudoku
Interactive sudoku game with high score tracking. Includes solution strategies.
http://www.braingle.com/games/sudoku/index.php

Count to Nine
Offers five difficulty levels, timer, solution, and printable view.
http://www.counttonine.com/

Daily Sudoku Puzzle
Offers daily timed puzzle and four difficulty levels. [English/Portuguese/Spanish/German/French/Italian]
http://www.daily-sudoku-puzzle.com/

Fiendish Sudoku
Free daily sudoku puzzles at five difficulty levels. Online solving grid with hints and step-by-step solutions.
http://www.fiendishsudoku.com/

Free Sudokus
Offers hints, solution checking and grids in sizes other than 3x3.
http://www.free-sudokus.com/

Goobix.com
Offers up to four difficulty levels.
http://www.goobix.com/games/sudoku/

GSudokr
Online sudoku puzzles with solutions, game instructions, and timing.
http://www.gsudokr.com/

Jaap Scherphuis' Generator
Java-based generator offers four levels of difficulty. Includes view of solution.
http://www.geocities.com/jaapsch/sudoku.htm

Number Logic
Offers a new timed game daily, with a validator and four difficulty levels.
http://www.number-logic.com

Paul's Pages
Offers random, crafted, and non-standard puzzles. Includes hints and import/export tool.
http://www.paulspages.co.uk/sudoku/

Play Sudoku
Registered users can save unsolved puzzles and high scores are kept at three difficulty levels. Also offers rules and tips for solving. [English/Russian/German]
http://www.play-sudoku.de/

Play Sudoku
JavaScript-based Sudoku, available for syndication on other sites.
http://www.geocities.com/binnyva/code/javascript/sudoku/

Puzzles4Free.com
Free sudoku puzzles daily for you to solve. New puzzles every day.
http://www.puzzles4free.com/sudoku/

Ridiculopathy - Sudoku Shuffle
Play with letters or numbers in the grid. Includes high scores, hints and move verification. [Requires Flash]
http://www.ridiculopathy.com/crappy_flash_games.php?gamename=sudoku

Seeing With C - Sudoku Solver
A solver program with an article explaining the algorithm used.
http://www.seeingwithc.org/sudoku/sudoku.html

Sudoku
Japanese puzzle game played by placing numbers in a grid so that each number only appears once in each row, column, and region. Offers three difficulty levels.
http://www.sudoku.name/

Sudoku by Froggy
Generates 2x2, 3x3, and 5x5 puzzles with adjustable level of difficulty.
http://www.orcapia.com/froggy/sudoku/

Sudoku Central
Offers daily puzzle for printing. Also includes archive, online solver, and solving tips.
http://www.sudokucentral.com/

Sudoku Fun Puzzles
A website representation of Sudoku, the broad sheet newspaper puzzle imported from Japan. Leaderboard lets players compare completion times.
http://www.sudokufun.com/

Sudoku Hints
Offers daily web-based puzzles with five difficulty levels. Includes solver, helper, and XML feed.
http://www.sudokuhints.com/

Sudoku League
League of online competitors. Scoreboard, rules, FAQ, hall of fame, and instructions. [English/Czech]
http://www.sudoku-league.com/

Sudoku Online
Online play with several different variants.
http://www.sudokuonline.ro/en/puzzle/

Sudoku Puzzles
Daily puzzles offered at four difficulty levels, available for play online or printed out. Includes rules and archives.
http://sudoku.com.au/

Sudoku Zone
Play sudoku puzzles online for free.
http://sudoku-zone.50webs.com

SudokuDave
Easy to very difficult puzzles that you can play online or print out.
http://www.geocities.com/da5id65536/SudokuDave/

Su-Doku.net
Offers daily puzzle, downloadable games, and instructions.
http://www.su-doku.net/

s.udok.us
A new Sudoku puzzle every day and an archive of old grids.
http://s.udok.us

Web Sudoku
Free puzzles with difficulty levels ranging from easy to evil. Provides print and online syndication.
http://www.websudoku.com/