Links to sites demonstrating visual illusions and other phenomena:

http://lite.bu.edu
Project Lite (Light Inquiry Through Experiments)

http://www.badastronomy.com/bad/misc/dark_side.html
(explores the science behind the appearance of the moon)

http://gandalf.psych.umn.edu/%7Ekersten/kersten-lab/
images/ball-in-a-box.mov
(a demonstration of the effects of shadow on the perception of motion)

http://visionlab.harvard.edu/Members/Alumni/ikuya/
html/memorandum/VisualJitter.html
(an interactive site exploring our perception of jittering motion)

http://www.cs.umb.edu/~ram/ArtAndVision/MachBandingApplet.htm
(an interactive site exploring Mach bands)

http://www.biols.susx.ac.uk/home/George_Mather/
Linked%20Pages/Motion/BM.HTML
(shows how little information we really need to perceive human motion)

http://humanities.lit.nagoya-u.ac.jp/~illusion/gallery/
kitaoka/soccer/index_e.html
(what is the true shape of each of these boxes?)

http://www.psychology.psych.ndsu.nodak.edu/mccourt/
website/htdocs/HomePage/Projects/Brightness/Troxler%20fill-
in/Troxler%20fade%20and%20fill-in.htm
(what happens if you stare at this disk?)

http://www-bcs.mit.edu/people/adelson/checkershadow_illusion.html
(illustrates how context affects what we see)

Links to sites providing information on the human visual system:

http://www.visionscience.com/
(a comprehensive overview of vision science)

http://www.yorku.ca/eye/thejoy.htm
(an overview of visual perception)

http://www.nei.nih.gov/health/index.htm
(information on eye health)

http://www.hhmi.org/senses/a130.html
(good tutorial on sight, hearing, and smell)

http://buster.cs.yale.edu/implicit/measure1.html
(how do social psychologists use your reaction to what you see to measure attitudes?)

http://www.choisser.com/faceblind/
(a personal exploration of the phenomenon of "face-blindness")

http://www.discoveryfund.org/anatomyoftheeye.html
(a primer on eye anatomy)

http://www.psc.edu/science/Miikkulainen/Miikkul.html
(an overview of the visual system)

http://webexhibits.org/causesofcolor/index.html
(great comprehensive discussion of the perception of color)

http://white.stanford.edu/~brian/numbers/
node1.html#SECTION00010000000000000000
(important numbers in vision science)

Links to sites exploring how other animals see the world:
http://www.ebiomedia.com/gall/eyes/nocturnal.html
(explores animal night vision)

http://cvs.anu.edu.au/andy/beye/beyehome.html
(a simulation of how honeybees see the world)

http://www.mammaleye.com/
(an overview of the mammalian visual system)

http://www.sbnp.org/Wetlands/text/00-7-2-4.htm
(a look at the wide range of animal eyes)

http://webexhibits.org/causesofcolor/17.html
(explores animal color vision)

http://www.pigeon.psy.tufts.edu/psych26/umvelt.htm
(in-depth overview of how animals see the world)
Links to sites presenting images from a wide range of the visual arts:

http://www.avam.org/index.html
(the American Visionary Art Museum)

http://www.artandoptics.com/
(David Hockney explores art and optics)
http://www.artistsineastlondon.org/home.htm
(photography from the United Kingdom)
http://www.eyestorm.com/saatchi/collection.asp
(the Saatchi Eyestorm collection)
http://www.bbc.co.uk/arts/news_comment/artistsinprofile/wynevans.shtml
(the visual art of Wyn Evans)
http://oursler.net/tonyoursler.html
(the visual art of Tony Oursler)
http://www.rodencrater.org/seeing/index.htm
(explores James Turrell's landscape art at Roden Crater)
http://www.ultrafuzz.net/index.html
(the visual art of Barney Haynes)