I don't think you can do justice to 70s metal without some Black Sabbath. Toss in Ozzy's first few solo albums as well. Diary of a Madman & Blizzard of Ozz are a couple of my all-time favs. Occult? Some would say so. Download some MP3s before you buy, if you're unsure.
While you're at it, check out Deep Purple. Their Machine Head album is also on my fav list. Hmmm ... also, try Iron Maiden, Blue Oyster Cult, Ted Nugent, ... how many options do you want?