Sudokus
Sudoku-X
Cage-Sum (aka Killer) Sudokus
MiniSum
Downloads
Christmas Puzzles
Sudokus - Easy (top), Medium (middle), Hard (bottom)
See also the small variant based on sums - click here or on MiniSum above.
In standard SUDOKU puzzles (as on the left), the aim is to place the digits from 1 to 9 in each small square so each row, column and 3x3 mini-array (surrounded by bold lines) contains each digit just once.
With Sudoku-X puzzles, it is also required that each main diagonal contains each digit just once. A 'correct' Sudoku-X will not be soluble unless use is made of the additional diagonal requirements (i.e. you will not be able to fill it in fully if you treat it like a standard Sudoku).
The Books page lists collections of both types of puzzles. The Downloads page offers a free Windows-compatible Player program for Sudoku/-X puzzles, as well as downloads of the puzzles featured here.
I also set Killer Sudoku puzzles (which, despite the name, are not necessarily difficult!). These involve Sudoku grids in which no squares are pre-filled in but in which meshes are used to surround given areas, the sum of all contained square values being indicated.