As I am Australian and this is an Australian site, can I draw your attention to my new online Sudoku Solver (and Tutor): www.philsfolly.net.au
Using some new logical techniques, this solver can crack even the hardest known puzzles. It is written in Javascript and is fully interactive. In contrast to some other solvers whose solutions for these hardest puzzles border on incomprehensible, the new techniques I have come up with are readily understandable and fully explained in the help items given for all techniques.
The program shines in demonstrating solutions to medium difficulty puzzles - the hard/diabolical puzzles that one finds in books and newspapers. It has a full implementation of fish, ALSs, POMs, URs and chains, so most puzzles are taken care of without reverting to the advanced techniques involving nets or contradiction.
Feedback on bugs or other problems would be appreciated
pjb