Craig Hickman’s Virtual Camera is an online application, or web site, that presents a camera whose settings you can control. As you change the settings the image on the simulated LCD changes, showing you how the setting changes affect the image. You can choose auto, program, aperture priority, shutter priority and manual modes as you would on your camera. The site behaves just as your camera would, allowing you to change the either the aperture, shutter speed or ISO depending on the mode you chose. You can also change the exposure value (EV). This is a great way to learn how all these settings interact to affect the image.
Here is a screenshot of the site.