The Neural Correlate Society hosts an annual "Best Illusion of the Year" competition, which they describe as "a celebration of the ingenuity and creativity of the world’s premier illusion research community."
Judges picked the top ten illusions, posted here in descending order of awesomeness according to the judges. It's a trip.
1. Shape From Stop Motion Only
"Can you see the forest for the trees?"
2. Sky Blue Cafe Wall Illusion
"A pigment of your imagination."
3. Dynamic Müller Lyer Illusion
Don't let the brackets shrink you down.
4. TILLA at the beach
It's all about perspective.
5. Partial Disappearance Illusion
Say goodbye to the roosters.
6. The Windmills of Your Mind Illusion
The spinning is all in your head. (Note: the music on this one f**king creepy)
7. Mask Induced Filling Out
Fill it in yourself.
8. The Material Inversion Effect
It'll turn that frown upside down.
9. The Shrink and Swell Illusion
Pairs well with Chopin.
10. Complementary Afterimage (Quantum Rainbow)
See what it's like to be colorblind.