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.