Puzzles

Okay, I don't know that for sure. According to their FAQ, there exist 6,670,903,752,021,072,936,960 possible completed Sudoku puzzles, and they only claim to have mere billions, divided into difficulty levels ranging from Easy to Evil.

In case you've been living under a rock since 2004, Sudoku is a puzzle that originated in Japan. You use logic to place the digits 1 through 9 in a 9x9 grid, so that every row, column, and 3x3 subgrid contains each digit exactly once. While Sudoku puzzles can be hard to solve, they are addictive - and easy for computers to generate, which explains the explosion of Sudoku in magazines, newspapers and websites in recent months.

The site, which is free, has an incredibly easy-to-use interface for their interactive puzzles. It loads quickly, and has no ads or flashy graphics. You can solve the randomly selected puzzle of the day or choose any one from their vast inventory. There is a "How am I doing?" button, which can show you where you've made mistakes if you run into trouble.

If you're a Sudoku addict, this site gives you an endless supply of the puzzles you crave. If you're not, you can easily become one. I can't think of any reason to go to any other Sudoku site - everything you could possibly want is here.