Here are films that changed the world, righted wrongs, pinpointed a moment in history, or simply shone a light on a previously unknown subset of society. (Availability subject to change. Films are unrated, except as noted.)
1. "20 Feet from Stardom" (2013) PG-13
This Oscar-winning doc shines a spotlight on the relatively unknown backup singers behind such superstars as Bruce Springsteen, Sting, Mick Jagger, and Stevie Wonder.
2. "The Act of Killing" (2012)
The director invited killers -- men who took part in the horrific purge that left more than 500,000 dead in Indonesia in the 1960s -- to reenact their crimes on film, resulting in a bizarre look inside the mind of men capable of mass murder.
3. "The Battered Bastards of Baseball" (2014)
Two filmmakers pay homage to their grandfather, who managed the Portland Mavericks, a defunct '70s minor league team. Scott Foundas of Variety wrote that the film is "so rife with underdog victors and hairpin twists of fortune that, if it weren't all true, no one would believe it."
4. "Berkeley in the Sixties" (1990)
In the '60s, Berkeley was the heart of the counterculture and the Free Speech Movement. This film, which was nominated for an Oscar and won the Sundance Audience Award, features archival footage of student activists, musicians, Beat poets and the officeholders of the day, including then-California Governor Ronald Reagan.
5. "Birders: The Central Park Effect" (2012)
Who's more colorful, the wild birds that call Central Park home or the human hobbyists – among them, author Jonathan Franzen – who spend their lives watching them?
6. "Blackfish" (2013)
An exposé of SeaWorld's treatment of their star killer whale, Tilikum, which led to worldwide denunciation of the theme park's practices and massive boycotts.
7. "Booker's Place: A Mississippi Story" (2012)
A follow-up to Frank DeFelitta's 1965 short film about African-American waiter Booker Wright, who talked candidly about dealing with racism in the South. Nearly 50 years later, Frank's son returns to Mississippi to document the results of that life-changing interview.
8. "Brother's Keeper" (1992)
Joe Berlinger and Bruce Sinofsky, who went on to direct the "Paradise Lost" films about the West Memphis Three and the Metallica doc "Some Kind of Monster," made this award-winning film about a 1990 murder in rural upstate New York in which a barely literate man may have killed his brother.
9. "Cave of Forgotten Dreams" (2011)
Werner Herzog was granted unheard-of access inside the French caves that contain the world's first cave paintings in this film that's won numerous awards.
10. "The Endless Summer" (1966)
The ultimate surf movie, complete with (of course) a surf rock soundtrack. Two surfers, go on an epic trip around the world looking for the perfect wave. (But not robbing banks.)
11. "Exit Through the Gift Shop" (2010)
Who else but street artist Banksy could tell the story of Thierry Guetta, a French immigrant in Los Angeles obsessed with street art?
12. "G-Dog" (2012)
"G-Dog" is Father Greg Boyle, a Jesuit priest who launched the largest, most successful gang intervention and rehab program in the U.S., Homeboy Industries.
13. "Gideon's Army" (2014)
Follows three black public defenders in the South who take on long hours, low pay and far too many caseloads. It won the Ridenhour Documentary Film Prize and the Candescent Award at the 2013 Sundance Film Fest.
14. "Hoop Dreams" (1994)
The film follows two poor African-American teenagers who are recruited by a prestigious, predominantly white high school basketball team, but must undergo a 90-minute commute and grueling practices. After nearly universal acclaim, there was an outcry when the film wasn't nominated for an Academy Award.
15. "How to Die in Oregon" (2011)
In 1994, Oregon became the first U.S. state to allow physician-assisted suicide. The documentary examines the right-to-die movement and tells the story of those who have chosen to end their own lives since it became a law. Won Grand Jury Prize for Documentaries at Sundance.
16. "The Imposter" (2012)
A fascinating, stranger-than-fiction story of a French man who passed himself off as homeless teenagers for years, finally pretending to be a long-lost 13-year-old from Texas. Despite striking physical differences, he was accepted by most of the family as their lost kin.
17. "Incident at Oglala" (1992) PG
Michael Apted directed and Robert Redford narrated this documentary about the murder of two FBI agents on a South Dakota reservation. Leonard Peltier was convicted of their murder, but many believe he is innocent. The case inspired the 1992 film "Thunderheart," also directed by Apted.
18. "John Waters: This Filthy World" (2006)
The maverick director of "Pink Flamingos" and the original "Hairspray" does a one-man, uncensored show in front of a live audience.
19. "Lost Angels: Skid Row Is My Home" (2010)
Catherine Keener narrates this profile of eight homeless Angelenos on Skid Row, where they manage to find refuge and hope for the future.
20. "The Loving Story" (2011)
The 1958 marriage of Mildred and Richard Loving was declared illegal in Virginia because he was white and she was black. Their case went all the way to the Supreme Court, leading to a landmark 1967 decision that legalized interracial marriage.
21. "Man on Wire" (2008) PG-13
This Oscar-wining documentary, about Philippe Petit's 1974 high-wire walk between the Twin Towers of the World Trade Center, is more thrilling -- and more moving -- than most feature films.
22. "More Than Honey" (2012)
A look inside the strangely compelling world of bees, beekeepers, and industrialized honey farms that boasts astonishingly beautiful macro-photography.
23. "Paris Is Burning" (1990) R
Before Madonna ever vogued, the ultra-fabulous drag queens of New York took part in fierce contests to replicate the cover of their favorite fashion magazine and win points for "realness." Its snub by the Oscars (along with "Hoop Dreams") prompted an overhaul of the Academy's selection process.
24. "Restropo" (2010) R
Sebastian Junger (author of "The Perfect Storm") and photojournalist Tim Hetherington documented the year they spent embedded with troops in Afghanistan. Hetherington was killed the next year while covering the Libyan Civil War.
25. "Sherman's March" (1986)
Ross McElwee set out to make a movie about General Sherman's "March to the Sea" during the Civil War, but after a rough breakup, decided to focus on his own tumultuous love life.
26. "The Square" (2013)
The film is about the Egyptian Revolution of 2011, which had its roots in Tahrir Square (also known as "Martyr Square") in Cairo, a common site for political demonstrations. It was nominated for an Oscar and received three Emmys.
27. "Stolen Seas" (2012)
The filmmakers traveled to some of the world's most dangerous places to make this documentary on Somali piracy, where they interviewed actual pirates, hostages and their relatives, negotiators, and experts on piracy and international policy.
28. "The Thin Blue Line' (1988)
Sure, "Super Size Me" prompted McDonald's to cancel their Super Size menu, but Errol Morris's film about a man serving a life sentence for murder, got his conviction overturned, thanks to his own look at the crime. Now that's the power of film. You can also stream Morris's doc, "Vernon, Florida."
29. "Virunga" (2014)
Amidst the civil war in the Congo, a few dedicated people risk their lives to save the last of the world's mountain gorillas.
30. "Waste Land" (2010)
This winner of more than 50 awards (including an Oscar nomination), is the story of artist Vik Muniz, who travels to the world's largest landfill to transform garbage into highly sought-after art. Would make a good double bill with "Trash Dance" (2013), about the "beauty and grace in garbage trucks, and in the men and women who pick up our trash."
31. "We Were Here'" (2011)
This look at how San Francisco coped with the AIDS crisis focuses on five people -- caregivers, activists, friends and lovers -- whose lives were forever changed by the disease.