Holy Sighting
Fixate on the four dots in the middle of the picture for about 30 seconds.
Then close your eyes and tilt your head back.
Keep them closed..., you will see a circle of light appear, continue looking at the circle...
What do you see?

Disappearing Dots
If your eyes follow the movement of the rotating pink dot, you will only see one color, pink.
If you stare at the black + in the center, the moving dot turns to green.
Now, concentrate on the black + in the center of the picture. After a short period of time, all the pink dots will slowly disappear, and you will only see a green dot rotating!
It's amazing how our brain works. There really is no green dot, and the pink ones really don't disappear.
This should be proof enough, our perception is stranger than we know.

More Changing Dots
There are only white dots in the image below,
but do your eyes agree?.
For fun, hide this message at the top of the screen,
and ask someone to count the number of black dots. :D

Gray intersections
A variation of the changing dots above,
the intersections of the white lines in the grid appear gray.

Same Shades of Grey?
The squares labeled A and B are the same shade of gray.
I found this one so hard to believe,
that I individually captured screen shots of each letter (using SnagIt),
then placed them side-by-side (see below).
Yep, there're the same alright, hard to believe but true!

These are actual, un-edited screen captures from the pic above.

Update 4/20/09: I learned that the above illusion is known as "Adelson's checker shadow illusion," and is credited to Edward H. Adelson, a professor at MIT's Dept. of Brain and Cognitive Sciences.  You can learn the science behind how it works here: http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html.
 

Moving or Still?
The image below appears to rotate counter-clockwise,
even though it stationary.
Using your peripheral vision will enhance the effect.

Illusive Message
There's a message in the image below, but the eyes need to adjust before it's readable.
The main method is increasing your viewing distance (by several feet).
Another helper is to pull the corner of your eyes as if you were Chinese.
If all's failed thus far, viewing the monitor from the side is perhaps the easiest way to see this all-so-important message!

Test Your Blind Spot

Alright, you can currently see both an X and a circle. Close or cover up your left eye. Now SLOWLY move your head closer to the screen and stay focused on only the X. As you get about six inches from the computer screen, you'll see that the circle has disappeared. You've just found your blind spot!

If you know of cool illusions not yet listed here,
please send 'em on over to dave@daverowland.net,
and perhaps they'll get posted.