Sudoku Learning Center is a web site designed to help people master a wide variety of solver techniques. It includes instructional text and specially designed puzzles and graphical hints to help individuals master Sudoku.
The techinques covered are hidden singles, block and row/column interactions, block and block interactions, naked subsets, hidden subsets, XY Wings, X-Wings, Swordfish, Coloring and Forcing Chains.
In addition, the web site has a "Dancing Links" solver for those that want solutions to puzzles not covered by the above techniques.
Besides the lessons on the various techniques, you may choose the types of puzzles you wish to solve. It allows you to select custom puzzles with just the techniques you wish to see in your puzzles. It's a great way to play Sudoku for fun:)
Hopefully someone besides me will find this useful I would appreciate feedback on the web site. It is still a work in progress and obviously needs more work. The web site http://www.sudokulearningcenter.com