Oh - I'd also suggest some Budgie. Their early stuff is pretty bloody heavy for the time, but also really interesting. Songs like Parents, Breaking all the House Rules and Breadfan are pretty good early heavy rock songs
I know some of you are thinking 'Why are these old bastards recommending all this old sh*t - this isn't metal' - If you like a genre, it's important to understand it's roots - and these guys (Sabbath, Beck's 'Truth' album, Cream, Budgie etc etc) are the roots of metal...
Why do you think us old guys who were influenced by Thin Lizzy, Led Zep etc etc, also listened to a lot of blues stuff - coz it was the roots of that sort of music...