Sudoku Wiz will generate millions of challenging Sudoku. It allows you to easily key in problems from other sources, save and print them. The Wiz will highlight key blocks for you and show (for each square) which solutions are logically possible. It gives you complete control over your puzzle environment, allowing you to change colors, turn bookkeeping and highlighting on or off, all with the press of a mouse key.
You don't have to be at your computer to use Sudoku Wiz. Suppose you have been working on a problem when you suddenly realize that you have to go to work (school/the doctor's/wherever). You just quickly print out an image of the current state of your puzzle, including highlighting and bookkeeping, and you're out the door!