CameraSim simulates a digital SLR camera - SLR Photography Demystified:
'via Blog this'
This is a brilliant little tool for exploring what all those manual settings on your camera are, and actually DO. Extra points for the 'use a tripod' button. (Generally speaking, it's wise to use a tripod ANY time you're using a longer lens - I often don't when I'm willing to experiment with 30 different shots, and there's no client to worry about. Your mileage may vary.)