Pretty decent book on how to solve Sudoku's. I got mine from the author and my wife has learned a lot from it, so I just bought one for my mom.

Quoted: Here it comes: a revolution in sudoku solving! This is by far the most complete guide to cracking these addictive puzzles ever produced, with tricks even the experts won’t know. While most books might have a few pages of introduction before proceeding straight to the sudokus, this one covers it all: hidden pairs, naked pairs, X-wings, jellyfish, squirmbag, bivalue and bilocation graphs, turbot fish, grid coloring, and chains. Every single one is here, and much more too, including the exclusive Gordonian logic methods (Gordonian rectangles and Gordonian polygons) that will turn even the hardest puzzles into a breeze. Of course, there are hundreds of sudoku for practice. A very special addition is a reprint of the very first sudoku ever published in 1979, from Dell Pencil Puzzles and Word Games magazine!