Winged Migration
No documentary has produced such beautiful images as this Jacques Perrin–directed meditation on the journeys of migratory birds. Shot on every continent, with the collaborative efforts of 450 people, including teams of bird handlers who lived 24/7 with goslings, the 2001 movie literally takes flight, filming the creatures at close range and offering us, for the first time, a real bird's-eye view.

Grizzly Man
On the surface, Timothy Treadwell's story is unsurprising: A self-appointed bear researcher is killed, along with his girlfriend, Amie Huguenard, by his subjects in Alaska. But Werner Herzog uncovered in Treadwell's handycam footage a fragile but ultimately agreeable character. The resulting film, 2005's Grizzly Man, culminates with Herzog listening to the recording of Treadwell and Huguenard's demise (the camera was rolling with the lens cap on). The look on Herzog's face is graphic enough. "You must never listen to this," he tells Treadwell's ex, Jewel Palovak. While Treadwell mostly projected human emotions onto wild animals, he tapped into something universal, too: the desire to find oneself in the wilderness after being rejected by the world.

Red Gold
Made in 2007 by young filmmakers Ben Knight and Travis Rummel, Red Gold is an ode to Bristol Bay, Alaska, site of both the world's largest sockeye run and a proposed open-pit mine that could obliterate the fish. The DIY film is less refined than the others on this list, but that's the appeal: The upstarts broke this story long before most major media outlets, and scored enough ominous quotes from tin-eared mining exec Bruce Jenkins to help spur an ongoing protest movement. "Just because you don't think this is a good idea," scolds Jenkins, "doesn't mean you're right." Unless, of course, you are.

Earth
The best wildlife and natural-history footage ever to come to the big screen. This is ultimately why you don't care that some 60 percent of it was poached from Planet Earth, the holy-s**t made-for-TV series that aired on the Discovery Channel in 2007: It's just as good the second time. Earth marked the launch of Disneynature, a label intended to help the entertainment behemoth reclaim its nature-doc glory days of the 1950s. The film focuses on three animal families—polar bears, elephants, and humpback whales—and certainly feels Disney. At its weakest moments, it's cute. But the James Earl Jones narration helps, the score soars, and—most important—it's just stunning to watch.

March of the Penguins
It's anthropomorphic, but don't call it a kids' film. March, which grossed some $77 million and won the 2006 Oscar for Best Documentary, is about survival. Over the course of a year, filmmakers Luc Jacquet, Laurent Chalet, and Jérôme Maison suffered through frostbite, an Antarctic blizzard, and reeking valleys of guano to capture the story of the emperor penguins. The birds endure far worse: 80-below temperatures, months without food, predatory leopard seals. It's a film packed with graphic moments of death and new life, lacking only the smell.