Explore vision on-line at these sites:

The Exploratorium is a hands-on science museum in San Francisco, CA. You can access some of their demonstrations on-line by following this link.

Brightness: http://persci.mit.edu/gallery.html

Motion: http://epunix.biols.susx.ac.uk/Home/George_Mather/Motion/index.html

Illusions: http://psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/index.html

General Vision: http://visionscience.com/

Several researchers and teachers have created sites with useful demonstrations of classic (and not-so-classic) visual phenomena. Here are a few:

Landrigan Lab at UMass Lowell

Stuart Anstis: http://psy.ucsd.edu/~sanstis/

Dale Purves: http://www.purveslab.net

Ken Brecher: http://www.bu.edu/smec/lite/perception/index.html

Akiyoshi Kitaoka: http://www.ritsumei.ac.jp/~akitaoka/index-e.html