I like this one.... it's been on PBS many times in recent years... "Alone in the Wilderness"
Alone in the Wilderness, DVD and VHS available, the story of Dick Proenneke
My Big Fat Diet:
My Big Fat Diet Part 1 of 3 - YouTube
Follow's the Namgi tribe returning to their ancestral diet. Not the flashiest, but one it is a documentary on one of the largest low carb studies conducted.
Also, while not a documentary Dr Eenfeldt's interviews of low carb doctors is interesting (most are on his site dietdoctor.com)
FYI on this web site: Watch Free Documentaries Online | Documentary Heaven
You can view free documentaries there (so the web site says).
A personal favorite is The Two Escobars, the ESPN film about Colombia & the drug trade (and the '94 World Cup).
Also amazing (especially if you like college football, and I don't normally) are the two documentaries ESPN did about SMU & U Miami. (Pony Excess is the SMU one, I forget the name of the U Miami one, but you can use the google). Both great TV.