The code for the below puzzle was written by Binny, an Opensource developer. I have just customised it a bit for my site

Online Sudoku

Online Sudoku is A javascript version of the popular japanese number game sudoku. This can be used to play sudoku online. Sudoku is a mind game and a puzzle that you solve with reasoning and logic. Fill in the grid with digits in such a manner that every row, every column and every 3x3 box accommodates the digits 1-9, without repeating any.