4. Deep Purple, 'Machine Head'
Before Deep Purple released Machine Head in 1972, most rock fans (at least in America) knew them as that Sixties band that covered Billy Joe Royal's "Hush" and Neil Diamond's "Kentucky Woman." That perception changed forever the moment "Smoke On the Water" hit the radio. This was almost a different band (fans dub them Deep Purple Mach II), and they were sensational – one of the few hard rock acts that could truly challenge Black Sabbath and Led Zeppelin. Machine Head was their most successful disc. It turned Ritchie Blackmore into a guitar god for generations of players, and about 10 billion garage bands got their start playing "Smoke on the Water." They tour to this day (minus Blackmore), but most of their fans are overseas and they rarely hit America.