Sudoku patterns

There are a few good sites for learning sudoku patterns:

• ScanRaid

  Many patterns described in text, including very advanced methods. Has a solver that applies techniques in succession so that you can see a particular technique applied to an actual puzzle.

• Sadman software

  Many patterns described in text.

• Angus Johnson

Update 2008-12-05: If I could just start to recognize these patterns, I'd be on my way to becoming a decent sudoku solver:

• X-Wing
• Simple Coloring
• Y-Wing
• Swordfish