PBS online has tons of shows to watch instantly, for free, including : Nova, Nature, The American Experience, Frontline, and Nova Science Now.
Nova Science Now is probably my favorite show offered on PBS online. It takes a different approach from many of the hour-long informational shows. Each 50-minute episode is devoted to one theme, but the show itself actually consists of four different 10 to 15 minute stories. The 15-minute segment is perfect for me. There are dozens of Nova Science Now segments to choose from too. I’ve watched segments on the intelligence of dolphins, the gene that contributes to senior citizens living a long healthy life, and the role sleep plays in memory. Check out the show here!