Update October 4: I noticed that the samurai blank grid might have been a bit too big to print, so I uploaded a slightly smaller version.
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I just figured that you might need some blank grids to print out so you could use them when you work on these puzzles. So here they are, download them, print them out using any image viewing software that support PNG (Portable Network Graphics) files and make sure you have a few of them if you’re working on a very tough puzzle!
By the way, PNG files can be viewed and printed very nicely with Firefox

Here are the grids:
Classic Sudoku grid (can also be used for Killer Sudoku)
Diagonal Sudoku (X) grid (can also be used for Killer Sudoku X)
Samurai grid