I like nothing more than watching a good heavy metal documentary, regardless of whether I care about the band really, so any recommendations would be most welcome.
A few from me, for what they're worth...
Headbanger's Journey, Metal Evolution, Global Metal - Sam Dunn's pretty great I reckon.
Get Thrashed: The Story Of Thrash Metal - A thrash nerd's delight.
Anvil! The Story Of Anvil - Funny, and quite moving.
Feel free to mention any you didn't like too!