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Bored with normal sudoku? I recommend the killer sudoku variant. There’s a nice page of daily puzzles available at killersudokuonline.com.
I have also written a cheat sheet for the puzzle, which you might find helpful.
And if you want something really different, you could try the Masyu (ましゅ) puzzle. It’s a bit harder to find these on the web (I think this is because the puzzles have to be hand-made.)
(Digression:) For some reason the Anglicisation of the puzzle name has gone for the accurate but misleading masyu. You should actually pronounce this mashu. (End Digression).
There are some samples here.