One of the finest openers can be found on American progband Happy The Man’s second album Crafty Hands:
Sky is red I don't understand, past midnight I still see the land.... Burn! Deep Purple: Burn (1974), Made in Europe (1975)
Not only a great opener but also one of the all time best first to second song transitions. The loud squealing end to this song leading into the flute driven "Talk to the Wind" is brilliantly unsettling
I believe this was the first time I tried out a headset previewing CDs in HMV (remember those?). Blew me away.
From the soft rock side of things comes the beyond-gorgeous, haunting "Snow Queen" from The City, kicking off Carole King's singing career