If you are a fan of our Facebook page, you probably saw this link yesterday. There is a fantastic DSLR simulator out on the web and it can be see here: http://camerasim.com/camera-simulator.html
You can practice using shutter priority, aperture priority, and full manual modes. You can adjust your focal length, iso, aperture, and shutter speed. To make things more interesting, you can also change the lighting (from indoors to sunny outside). Finally you can adjust the distance you are standing from the model.
The simulator gives you a view similar to what you would find in your viewfinder and allows you to properly meter your photograph. The truly great thing about this simulator is that you can try out different settings over and over to truly learn what each thing does.
I am currently thinking about designing an online training course around using this. Let me know what you think!