I was reading James' blog when he mentioned that Paint by Numbers is more fun than Sudoku. I didn't believe him, but I gave it a try and MAYBE he's right! I REPORT, YOU DECIDE: http://pbn.homelinux.com/pbn/index.html
Everyone should read my blog. And I'm totally right about Paint By Numbers. Just ask Feely. Feely loved Mario's Picross. I love Mario's Picross. I love buying Games magazines, doing the Paint By Numbers, and ignoring the rest of the magazine. They're great.
Paint by numbers are great. They originally appeared in GAMES magazine via a company called Conceptis Puzzles.
Conceptis has developed a few variations on the theme, all of them hopelessly addictive: Pic-a-Pix (same as the paint by numbers CRZ linked to), Link-a-Pix, and Fill-a-Pix.
Here's the appropriate linkage. Except for a few puzzles, you do have to create an account and sign in to play. Last I checked, though, registration was free and gives you access to new puzzles every week.
I have had to stop doing these things cold turkey on a couple of occasions when finishing them became far more compelling than all of the things I was supposed to be doing. A word of advice: don't start anything bigger than 20x20 unless you've got some serious time on your hands.