Everyone's been talking about Sudoku Puzzles, and at first I didn't see what the fuss was about. But Ana's laid up this week so I snagged one of Will Shortz Sudoku puzzle books at Border's the other day for her to do, read the introduction myself and tried a few and they're fun! It's like analog Tetris or Lumines fun, really! :-)
Of course, Wikipedia has all the details on the history, how to play, etc. A quick search found an online Web Sudoku version for you try out. And I also found a mobile version which rocks - I bought it last night and I spent several hours messing with it last night. Read that again: Hours. Feet up on the couch with the television on, solving puzzles on my phone until way too late in the evening. Pretty cool.
I've actually seen the web version before, but didn't think much of it. Make sure you read the bit on Wikpedia about how to solve the puzzles using reverse elimination, and row/column scanning. That's the part I didn't get at first, which made it much more accessible.
Now... someone needs to come up with a online massively multi-player version. :-) [update: Looks like Sony is releasing multiplayer Sudoku for the PSP this December. ROCK! ]