I just came across this great deal at Amazon. The list price is $99.98 and now it is on sale for $15.49! Definitely a fantastic film at a great price! Planet Earth: The Complete BBC Series (HD DVD)
8/5/09 Update: Amazon is sold out, but there are still some available from non-Amazon sellers on the website.
8/18/09 Update: Amazon has the Blue-Ray version of Planet Earth on sale for $39.49.