There were other bands kicking out the jams for the Devil before Black Sabbath, oh yes. Maybe not metal, per se, but at least one American and one British band were dropping some flutey, trippy-dippy acid folk silliness in the name of the Dark One at least a couple months before Ozzy and Co. ever started melting faces under the Sabbath banner, those bands being Coven and Black Widow, respectively.
Coven was from Chicago, and confusingly enough featured a bass player named Oz Osbourne (no relation). Their debut album is more curios than mind-bending psychedelia, with pretty standard folky jams being the norm -- albeit with lyrics about being a slave to Satan rather than peace and friendship. Also, Coven themselves perform a REAL, LIVE BLACK MASS on Side B! Scandalous!
Speaking of scandal, Black Widow was a band who loved negative press, and was demonized by the UK media during their 15 minutes of fame in the late 60's and early 70's. They professed their love for Satan and took pictures of themselves holding human sacrifice rituals, which in 1970 was not really OK in British society. If I had to choose between these albums, musically speaking, I'd have to give it to Black Widow. They sort of capture a freaky, "dancing-naked-in-the-woods" vibe that I can get behind 100%. Good stuff.
DRINK OF MY BLOOD, SWEET SATAN
COVEN - WITCHCRAFT DESTROYS MINDS AND REAPS SOULS (1969)
BLACK WIDOW - SACRIFICE (1970)