Jigsaw Puzzles:  A Brief History:  Another retail site, but has an interesting article on the history of jigsaw puzzles

Puzzle Museum: Wonderful site with lots of puzzle info and pictures

Cofanette by Miguel Berroco:  This page has close up pictures of Il Cofanetto, the Berracol puzzle place setting that the Professor and Kate used for their lunch in The Sudoku Murder.  You don't want to miss a good look at this fascinating construction.

Mathematical Association of America:  This site has a Sudoku page and interesting links.

The 15 Puzzle:  A true story.

For mysteries

Mystery Lovers Corner:  News, reviews and contests

Sisters in Crime:  Official site of Sisters in Crime for NY, CN, and NJ

Mystery Writers of America:  Official site

Kiss of Death Chapter of RWA:  For RWA members who write mystery, thrillers and suspense