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. (http://www.123opticalillusions.com/pages/lilac_chaser.php)
"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. (http://puu.sh/iunu)
"Find the monkey via the grooves in the picture"
Partially NSFW: Double Picture Illusion (http://www.123opticalillusions.com/pages/double-image-illusion.php)
No hints on this one, but read the bottom after you've analyzed the photo. :P
(http://upload.wikimedia.org/wikipedia/commons/thumb/0/0d/Ski_trail_rating_symbol-blue_square.svg/600px-Ski_trail_rating_symbol-blue_square.svg.png)
I like this one. It's a circle, disguised as a square.
The glass and the woman illusion always gets me.