Deep Purple
"Machine Head" (Vinyl)

Released in 1972, this album is cited amongst the influential albums in the development of heavy metal.
Perhaps more than their music, their image as a bunch of dark, long-haired fellows did more to create a mystique that would evolve into the habitat of metal.

This album includes the band's biggest hit, 'Smoke on the Water' and a lot of Hammond organ fed through a Marshall half stack.

I'll have to give this a few more listens, because unlike Sabbath's 'Paranoid,' this is the first time I've ever heard this album in its entirety.  It's a little premature for me to hint at it's importance to me.