I have to admit it. I just love optical illusions. I remember buying books full of them when I was a kid, and sharing them with anyone I could find.
Now, an incredibly complete collection of illusions called Eye Illusions has come to the iPhone and the iPad. For this review I've tested the iPhone version, which sells for US$0.99.
The illusions are in categories, like disappearing objects, weird lines, color illusions, etc. The app has something my books didn't have -- video. There is a great collection of videos of seemingly impossible objects. You watch the video, and then you get a look behind the scenes to see how the illusion was accomplished.