Unappreciated rock bands...

Really unappreciated:

Sir Lord Baltimore

Captain Beyond

Warhorse

UFO (the first line-up, before Schenker...)

Silverhead


...and not really underrated then, but now nearly forgotten:

Black Oak Arkansas

Black Oak Arkansas - Jim Dandy (Live)

BLACK OAK ARKANSAS RACE WITH THE DEVIL

Hot And Nasty Black Oak Arkansas Jim Dandy