So you love your Sudoku, in fact, you are getting pretty good at it! Truth to tell it's all getting a bit too easy - 'fiendish' puzzles just aren't that scary any more, 'devilish' just isn't that hot, 'migraine' doesn't even give you a headache. You are ready to go onto the next level.

Super Sudoku
The first step up is the 16 by 16 grid, sometimes called Super Sudoku. Instead of 1 to 9, the grid consists of 16 squares either with numbers 1 to 16, or numbers 1 to 9 then letters A to G. The principle is the same as the classic Sudoku, just more of it.

Sudoku X
Then there is Sudoku X, 9 by 9 puzzle grids again, but instead of just using the numbers 1 to 9 in each square, row and column only once, the diagonals of the whole puzzle must also contain 1 to 9 only once. There is a special Christmas edition of these books by Christopher Monckton, cutely entitled Sudoku X-mas.

Samurai Sudoku
Also called Gattai-5 Sudoku, this is a variation on the 9 by 9 grid theme. This time the puzzle consists of five grids, one in the centre and the other 4 overlapping each corner grid of the central one. This means that your numbers must be placed correctly for all the five puzzle squares.

Dion Cube
If you are looking for the ultimate challenge try three dimensional Sudoku - the Dion Cube. This 'Extreme Sudoku' puzzle was developed by Michael Mepham, who compiles Sudoku puzzles for The Daily Telegraph. This is truly fiendish. Imagine 9 Sudoku puzzles piled up on top of one another. Not only must each digit appear only once in each row and column of each separate puzzle, but once only in each vertical column and on each face of the cube too.

There ought to be something there to appeal to the most jaded Sudoku enthusiast, and get you reaching for the headache tablets once more.