Here's my simple entry for the challenge:
http://www.mechanicalcat.net/tech/sudoku_solver.py
You'll need [url="http://www.python.org/"]Python[/url] installed to run it.
Apparently won't solve puzzles of fiendish complexity, but I've not found one it doesn't solve yet. The addition of some furher solving rules, or possibly just a brute-forcer at the end, would fix that. I'm not interested in brute-forcing Sudoku though - that's just too easy.