[1]
http://www.miniclip.com/games/sudoku/en/
[2]
http://www.suduku-online.com/
[3]
http://www.foxfordservices.co.uk/Home/Free-Online-Sudoku-Solver.asp
If that’s too easy for you, try the grid of 16 x 16 = 256 squares
http://royal-sudoku.freegames4rest.qarchive.org/
If that’s too easy for you, try three dimensional suduku, 9 x 9 x 9 = 729 cubes.
If that’s too easy for you, try three dimensional suduku, 16 x 16 x 16 = 4096 cubes.
If that’s too easy for you, try some shapes other than cubes.
