Today is National Illusion Day. Well, no, it's not really. But it should be. If there was ever a need for a day like National Illusion Day it's today. Of course, there's always April 15th, tax day, in which there's the illusion that your tax dollars were yours in the first place and, in the hands of the government, will do untold good for the nation/state but that's different.
I found a great video out on the site Mighty Optical Illusions (a little over-the-top but often has good stuff). It's a demonstration of 10 popular optical illusions in two minutes.
P.S. For those of you that like the Dragon illusion, there's a printable foldable version here.