Interesting article on rating the difficulty of Sudoku's and various solving methods (including a short backtracking program written in Ruby).

My friend Roy's new puzzle book. You can pre-order from Amazon now.

Quoted: Amazon.com: Who-doku: Sudoku with Personality: Books: Roy Leban by Roy Leban

My sister, Catheryn, is hooked on these. Tired of vanilla Sudoku? Go Samurai Sudoku!

Quoted: Samurai sudoku puzzles consist of five overlapping sudoku grids. The standard sudoku rules apply to each 9 x 9 grid. Place digits from 1 to 9 in each empty cell. Every row, every column, and every 3 x 3 box should contain one of each digit.

redotting: Catheryn

Quoted: Veit Elser, Cornell professor of physics, has found that an algorithm developed to process X-ray diffraction data also solves Sudoku puzzles.

February 2006 Article (and source code) for an algorithm using bipartite graphs for Sudoku solutions.

July 2005 paper describing a graph-based algorithm applicable to Sudoku puzzles.

Quoted: We apply our path and cycle finding algorithms in a program for generating and solving Sudoku puzzles, and show experimentally that they lead to effective puzzle-solving rules that may also be of interest to human Sudoku puzzle solvers.

Excellent article on the history and mathematics of Sudoku.

I've been thinking about explicit logic strategies for my solver - this site has some explanations I haven't seen before (X-Wing) and (Sword-Fish) - though I've used the former in manual solves.

Quoted: Sudoku Solver by Scanraid Ltd. Shows the logic behind solving Sudoku square by square.