Dimensions: A Beautiful Movie About Math

I'm always on the lookout for educational materials.  Today, I found Dimensions.  It's a two-hours movie with 9 chapters, describing 2-, 3-, and 4-dimensions worlds, complex numbers, and other topics.

It's free, filled with nifty graphics and animations, licensed under a Creative Commons license, can be viewed online, or downloaded with subtitles.

If you like Escher's art, or are curious about the fourth dimension or complex numbers, you might want to take a look.  For an overview of the contents, see this.