I found this excellent tool, DSLR Simulator online which lets you to take photograph with different SLR controls. You can adjust lighting, Distance, Focal Length, ISO, Aperture and Shutter speed.
It lets you try your skills and provide you with the comments on the photographs clicked. It is a pretty good Camera Simulator and the author has promised to release more picture options. It is fun use this DSLR sim. The original page is here. The author has published the SLR sim as App for all iOS devices.
DSLR Simulator / Camera Simulator
Feel free to provide your comments. Hope you liked the simulator.