I turned a friend of mine on to Sudoku awhile ago, but why pay for Sudoku books when there are free Sudoku generators for both the Palm and Pocket PC platform?
For the Palm, there is Sudoku 1.2 which is very thorough considering its freeware (the author does include a button on the webpage to PayPal him donations if you are so inclined).
For the Pocket PC, there is Sudoku Solver 1.1.