www.periodicvideos.com

The periodic table is a way of representing the 118 elements (one of which, #117 Ununseptium, has never been seen and apparently will decay in a few nanoseconds if it is ever formed). I like this site from the University of Nottingham in England, that links each cell in the periodic table to a charming YouTube video about each one of those elements. The scientist with the wild hair is great.
I linked the video for sodium here. It's a pretty random choice, but this is a typical and quite amusing video.