When we recently purchased our Playstation 3, we began watching the Planet Earth television series on Blu-Ray, and we have loved it. Not only is it fascinating and informative about one of our favorite topics, nature; but it looks incredible in high-definition and on a nice television screen.
Basically the producers of the show take one ecological niche (e.g. mountains, caves, fresh-water) and devote an hour to exploring the geology, ecology, plant and animal life to be found in those niches. It's a pretty incredible show.
Quick vote: Informative and classy, this show is best viewed in high-def.