An early classic of the genre revels in the gonzo, bone-headed idea of metal: Though This Is Spinal Tap was a (loosely scripted) mockumentary, its status as a legit document of the dazed and confused metal lifestyle is secure: Eddie Van Halen claimed "Everything that happened in that movie happened to me." Though it's clearly a joke -- a thoroughly and mercilessly funny one -- the film "taps" into what makes metal fun, while cleverly skewering the idea of anyone taking it too seriously.
Heavy Metal Parking Lot (1986) is a classic, a testament to the youthful spirit of metal, with such scenes as a spandex-wearing adolescent shouting that Madonna's "a dick" and punk rock "should be on Mars."
Penelope Spheeris' Decline of Western Civilization 2: The Metal Years (1988) looked at the Sunset Strip scene that gave rise to such glam metal bands as Poison and Guns N' Roses. Favorite part? A surprisingly coherent Ozzy Osbourne cooking breakfast in a bathrobe, and Paul Stanley of Kiss doing his interview from a satin-covered bed, covered in a tangle of lingerie-clad groupies.
The 2000s saw the art form expand and grow: Metal: A Headbanger's Journey (2005) was created by 31-year-old headbanger-turned-anthropologist Sam Dunn as he explored heavy metal's cultural impact and its fans' devotion. I love how it breaks through heavy metal stereotypes. Heavy Metal in Baghdad (2007) flips the concept of the Decline of Western Civilization 2: The Metal Years, showing a different side of heavy metal -- the other side of the world. In Iran, wearing one of your favorite heavy metal band's shirts could get you thrown into jail.
Also, I can't forget DimeVision, which presents Pantera's Dimebag Darrell as a sort of heavy metal Walt Disney who showcases home videos, pranks and mind-blowing riffs with constant access to an open bar. Or Pantera: 3 Vulgar Videos From Hell, a hell-raising collection of Pantera's home videos, live concerts, and everything in between.