Recently I have been introduced to a wonderful type of puzzles called "Bossanova". The rule is ridiculously simple and crystal clear and elegant just like Sudoku and I guarantee the enjoyment level is also similar, if not more.
Here is the original Japanese blog page where these puzzles are released:
http://h-syouyuyaki.blog.drecom.jp/category_21/
The author is Mr. 帆立 (Syota Abe).
Here is a forum page where the rules were discussed and I also posted some solutions for the sample puzzles:
http://www.djape.net/sudoku/forum/viewtopic.php?t=1151
Here is a guide written by yours truly on how to solve these puzzles:
http://www.djape.net/sudoku/forum/viewtopic.php?t=1155
Enjoy!