Sudoku Mania CD-ROM
You could buy a whole shelf full of Sudoku products, but they won't have as many puzzles as this one. Sudoku Mania contains about 300,000 Sudoku puzzles, plus a puzzle generator to create literally an infinite number more! You can print or solve the puzzles on-screen, and there are 4 levels of difficulty, plus a timer. There are hints if you get stuck, and optional "pencil notes". Any puzzle you don't finish can be saved and completed later. Sudoku is simple to learn, yet takes a lifetime to master, and this is one CD-ROM you could play for a lifetime!