What is your favorite optical illusion?

[xSalashawty]

Yes..these things. They're awesome. <3

If you don't know what they are, then I will facepalm. Other than that, post some interesting illusions you have! (It's probably best that you put the link and not the picture, along with a description of what's about to be seen)

Pac-Man/Lilac Chaser illusion.
"Lilac chaser is a visual illusion, also known as the Pac-Man illusion. When one stares at the cross for about 20 seconds or so, one first sees a gap running around the circle of lilac disks, then a green disk running around the circle of lilac disks, then a green disk running around on the grey background, the lilac disks having disappeared."

Finding shapes in stuff.
"Find the monkey via the grooves in the picture"

Partially NSFW: Double Picture Illusion
No hints on this one, but read the bottom after you've analyzed the photo.

[Supersonic196]

I like this one. It's a circle, disguised as a square.

[Super Sonic Boom]

The glass and the woman illusion always gets me.