Well, I posted this a week or so ago for Earth Day, but in Itunes format! Now it's available thru Amazon as well:

Planet Earth - Vol 1 FREE download in HD 720p via Amazon VOD
Stream it, or download it, and enjoy the movie in 720P HD for free from Amazon Video on Demand.
You don't need an account to view it, but you do need an account to download it in 720P w/5.1 sound.

Amazon.com: Planet Earth [HD]: Season 1, Episode 1 "From Pole to Pole [HD]": Video On Demand