Hard Rock: when you mention it, you immediately think of Led Zeppelin and Deep Purple (as well as Cream and Free)... I would like to propose some examples of lesser-known bands or those not directly associated with the genre.
38 - A̤r̤m̤a̤g̤e̤d̤d̤o̤n̤-̤A̤r̤mageddon-- Full Album HQ 1975