Well I have three right now, that I'm using...Hope This Helps
Mensa's Guide to Solving Sudoku, Had to Go Online to Order This Book
52 Steps to Become A Sudoku Master
A step by Step Guide to Solving Sudoku by Robin Wilson.
The Mensa book is very good and gives you a very detailed explaination of how to solve the puzzles and gives you puzzles after every chapter to pratice the technique you learned, only one drawback is that the puzzles are very small in the book.