Black Sabbath, Led Zeppelin, Deep Purple: three great rock bands, all three with blues & jazz roots ("Wicked World" is pure jazz), but each one with its own distinctive style.

As opposed to today, when almost every band sound alike.

PERSONALLY, I like Black Sabbath better, but the other two are present on my record collection as well (I have all Led and almost all DP´s, except for the real sucky ones like Masters and Slaves).