Colour blindness simulator for Mac OS X
Sim Daltonism is a very handy little application for Mac OS X that lets you simulate various types of colour blindness in real-time. Just launch the app, select the type of colour blindness to simulate, move your cursor to the area you want to check, and Sim Daltonism will display the result in a floating palette.
Needless to say, using an application running on your own computer is much more efficient than using the web based colour blindness simulators out there. (via Wait till I come!)