9x9, 6x6 and Samurai Sudoku
   Offers classic Sudoku and variants, as well as an online solver.
   http://www.sudoku.4thewww.com

Automatic Sudoku solver
   Web-based application for automatic Sudoku solving. After setting a part of grid the puzzle will be automatically solved.
   http://www.jarek.cz/en/logical-puzzles/sudoku/automatic-solver/

BBC News: The puzzling popularity of Su Doku
   Article by Paula Dear. Covers history in Japan and the UK and compares to the Rubik's cube craze of the 80s.
   http://news.bbc.co.uk/1/hi/magazine/4469719.stm

Christiaan Olie
   Personal page describing Sudoku, rules, strategies, and offering puzzles to print. [Dutch/English]
   http://familieolie.filternet.nl/sudokuenglish.html

Daily SuDoku
   Offers daily printable puzzles of varying difficulties, including Sudoku for Kids. Also offers archive of past puzzles, tool for rendering custom puzzles, FAQ, and books for purchase.
   http://www.dailysudoku.co.uk/

Daily Sudoku
   Offers a different printable puzzle each day. Also includes solutions and FAQ.
   http://www.daily-sudoku.com/

Dan Rice's Sudoku Blog
   Blog discussing techniques for creating and solving puzzles, including hard puzzles. Also offers a daily puzzle.
   http://sudokublog.typepad.com/sudokublog/

Flying Frog Consultancy
   This web page describes a 19-line (769-byte) OCaml program that solves Sudoku puzzles.
   http://www.ffconsultancy.com/free/sudoku/

Free OnLine Sudoku
   Over 200000 sudoku puzzles to play or print for free. No registration needed however you can play a rank game if you register.
   http://www.gosudoku.eu

Free Sudoku Puzzle
   Articles on the game, its history, and where to find it online.
   http://www.freesudokupuzzle.net/

Gaby Vanhegan
   Daily and random puzzles at six difficulty levels, Flash and JavaScript solvers, solving techniques and glossary of terms.
   http://vanhegan.net/sudoku/

Grant Gibson
   Offers syndicated puzzles for websites as well as print publications.
   http://www.grantgibson.co.uk/sudoku/

Hirofumi Fujiwara's Sudoku
   Offers a tutorial for creating puzzles, a Java-based solver, and links to other resources. [English/Japanese]
   http://www.pro.or.jp/~fuji/index-eng.html

Information For Beginners
   Collection of printable grids, ordered by difficulty level. Solutions provided. Includes rules and solving methods.
   http://www.forbeginners.info/sudoku-puzzles/

Knight Features
   Publishing syndicate in the UK and Ireland. Offers several variations, including classic, colour, kids, and Sudoku Word.
   http://www.knightfeatures.com/KFWeb/content/features/kffeatures/puzzlesandcrosswords/KF/Sudoku/Sudoku_Classic/sudoku_classic.html

Maths Is Fun
   Offers a number of applications and solvers for a variety of platforms. Also offers custom puzzles.
   http://www.mathsisfun.net/puzzles.htm

Minimum Sudoku
   A project collecting Sudoku with the smallest number of givens that are still uniquely solvable. Offers the puzzle for download in text format.
   http://www.csse.uwa.edu.au/~gordon/sudokumin.php

My Days Are Numbered
   An article by Seth Stevenson offering a brief overview of Sudoku.
   http://www.slate.com/id/2119796

One Sudoku - one day, one sudoku
   Daily international competition - charts by countries and by users
   http://www.one-sudoku.com

Play Sudoku
   Flash version of the Sudoku game. Also offers solution.
   http://www.play-sudoku.com

Prize Sudoku
   Offers competitions for prizes. Traditional Sudoku, Godoku (letters) and Super Sudoku (16x16).
   http://prizesudoku.com/

Puzzle Bus
   Offers a daily puzzle, books, software, and related merchandise. Also offers puzzles for syndication.
   http://www.puzzlebus.com

Scanraid LTD Search Technologies
   Sudoku Solver by Andrew Stuart. Shows the logic behind solving sample games square by square.
   http://www.scanraid.com/sudoku.htm

Simple Sudoku Solver
   JavaScript brute force solver.
   http://homepage.ntlworld.com/valleyway/solver.html

Sky One
   Information on UK-based cellular provider's world-record largest Sudoku puzzle and accompanying contest.
   http://www.skyone.co.uk/programme/pgefeature.aspx?pid=48&fid=129

Solve My Sudoku
   Solves puzzles based on inputted information.
   http://www.solvemysudoku.com/

Solving Sudoku
   Step by step guide to solving sudoku puzzles. Goes from basic to advanced techniques.
   http://angusj.com/sudoku/hints.php

SuDoKu-Cracker
   The SuDoKu-Cracker only creates puzzles with a "unique solution". The built-in Sudoku-generator has six different levels of difficulty and can generate many (millions) different puzzles. All puzzles can be printed, saved and opened again.
   http://www.ksaw.no/sudoku?l=en

SuDokuMate
   SuDokuMate is a SuDoku Helper (not a Solver) that replaces pencil and paper to aid solving.
   http://www.sudokumate.com/sudokumate.asp

Sudoku
   Generates and solves classic and X-Sudoku Problems. Diverse options and an integrated help facility makes this program best of class.
   http://home.arcor.de/clemens-pichl/Sudoku.htm

Sudoku Addict
   Offers printable grids and solution walkthroughs.
   http://www.sudokuaddict.com/

Sudoku Helper
   Free online helper application. Shows options for each square, and allows backtrack, restart, or save.
   http://www.pewterweb.com/main/sudoku/nonform/Sudoku.htm

Sudoku Online
   Includes Sudoku tips and strategies as well as a downloadable game and a 3D Sudoku puzzle.
   http://www.sudoku.org.uk/

Sudoku Online Solver
   Free online generator, solver, and helper. [English/French/Spanish/Polish]
   http://sudoku.friko.net/

Sudoku Place
   Offers daily puzzle in PDF format. Includes archive, FAQ, and a "dozen" variant.
   http://sudokuplace.com/

Sudoku Puzzles
   Free daily puzzles with five difficulty levels with their solutions. Also offers guide to solve Sudoku puzzles.
   http://www.sudokupuzz.com

Sudoku enumeration
   Several programs in different languages for analyzing possible Sudoku combinations.
   http://www.shef.ac.uk/~pm1afj/sudoku/

Sudoku-san
   Free daily puzzles with four difficulty levels. Also offers a solving assistant and downloadable e-book collections for purchase.
   http://www.sudokusan.com/

Sudoku.com
   Includes an overview of how Sudoku is solved, a monthly contest and a downloadable Sudoku game. Also includes a kids section and discussion forums.
   http://www.sudoku.com/

SudokusWeb.com
   Free daily printable Sudokus. Also offers history, rules, and solving techniques. [English/Spanish/French/Catalan/German/Portuguese]
   http://www.sudokusweb.com/

Sudoweb
   Free daily puzzles with five difficulty levels. Also offers printable e-book.
   http://www.sudoweb.com

The Economist: Do you sudoku?
   Article on the puzzle's popularity in the United Kingdom and elsewhere.
   http://www.economist.com/displaystory.cfm?story_id=3992476

The Guardian: So you thought Sudoku came from the Land of the Rising Sun...
   Article by David Smith covering the puzzle's origins as "Number Place" by Dell Puzzle Magazine in New York in the 1970s.
   http://observer.guardian.co.uk/uk_news/story/0,6903,1484328,00.html

The Guardian: Sudoku fever grips UK newspaper readers
   By Stephen Brook. Article covers how the UK craze got started.
   http://media.guardian.co.uk/site/story/0,14173,1480828,00.html

The Heebie Su Doku Site
   Offers a glossary of terms, links to puzzles and variants, and tips for solving.
   http://sudoku.toplisted.net/syndicate/feed.php?syndtype=top&syndid=1648

The Sudoku Grandmaster
   Self-styled Grandmaster offers tips on life as Sudoku, humorous claims of achievement, and a daily puzzle.
   http://www.sudokugrandmaster.com/

The Times Sudoku
   Daily sudoku and killer sudoku puzzles from The Times newspaper, London.
   http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/games_and_puzzles/sudoku/

Universal Press Syndicate
   Offers monochrome and color grids and variations for online and print syndication. Information on syndication as well as an interview with creator David Bodycombe.
   http://www.amuniversal.com/ups/features/sudoku/

Vegard Hanssen's page
   Offers a database of crafted puzzles, organized by difficulty. Also offers FAQ and forum. [Norwegian/English]
   http://www.menneske.no/sudoku/eng/

Wikipedia: Sudoku
   An encyclopedia entry describing the rules, history, strategies and variants of Sudoku. Notes that these are a type of "latin square" which have been analyzed since ancient times.
   http://en.wikipedia.org/wiki/Sudoku

World Sudoku Championship
   Information on the 2006 World Sudoku Championship held in Italy. Includes background information, events, results and FAQ. [English, Italian]
   http://www.wsc2006.com/

Yosmany.net
   Offers HTML to add a JavaScript-based puzzle to any site. [English/Spanish]
   http://sudoku.yosmany.net