Hey you with the iPad! Do you like science? Do you have a kid who likes seeing cool optical illusions? If any of these are true you should check out Color Uncovered by the Exploratorium. It's a free app and it's pretty cool. There's stuff about color temperature, a fascinating article about how Monet paint's water lilies as blue because cataract surgery let him see ultraviolet light that most of us don't, and that sort of thing. There are little videos that you can watch and simple animations to explore topics like afterimages and those sorts of illusions that reveal the weird shortcuts our optical processing uses.

It's aimed at a younger audience and it's not something that takes more than an hour or so to flip through but it is well done and there were several articles that taught me things I didn't know before. And like I said, it's free so it only costs that hour of your time. Check it out!