Tiling and Patterns, Grunbaum.Book of Numbers, Conway & GuyWinning Ways, Conway, Guy, BerlekampInquisitive Problem Solver, Vaderlind, Guy, LarsonUnsolved Problems (in Geometry, or in Number Theory) -- As a general topic, I think it's good for kids to know that not everything has been solved.In Pursuit of the Traveling Salesman, CookTaking Sudoku Seriously, RosenhouseCRC Standard Mathematical Tables and Formulae Mathematica Guidebooks, TrottThe Big, Big, Big Book of Brainteasers, GrabarchukScott Kim's collected Discovery columns would be fantastic, if published.100 Strategic Games, JorisGems of Geometry, BarnesThe Zen of the Labyrinth, Phillips Online: MathWorld, Wikipedia, Burr Tools, Golly, Wolfram Demonstrations Project, Kadon Enterprises, mathpuzzle.com, Fractal Extreme, OscarPuzzle (on youtube), Vi Hart's youtube channel, Robert Abbott's logicmazes.com, Andrea Gilbert's clickmazes.com. Those will keep him busy for awhileEd Pegg Jr