In Rock - Deep Purple

While this wasn't Purple's debut album (it was their third or fourth studio album, I believe), In Rock is a blistering change to Rock/metal music by this band (Before this they played more poppish rock). Two of Purple's most well known songs are from here, Speed King & Child In Time. An extremely solid album. There is also a 25th Anniversary re-release of this album with twice as many songs, but I haven't gotten that one.