David Chen's List: Apple

Command-Shift-3  Capture the screen to a file    Command-Shift-Control-3  Capture the screen to the Clipboard    Command-Shift-4  Capture a selection to a file    Command-Shift-Control-4  Capture a selection to the Clipboard

Command-Option-esc  Force Quit    Command-Shift-Option-Esc (hold for three seconds)  Force Quit the front-most application (Mac OS X v10.5 or later)