Before Xanadu, even before Grease, there was Toomorrow which features 21 year-old Olivia Newton-John and three guys as the "rock group" Toomorrow and their sci-fi adventures. Produced in 1970 by Don Kirshner, creator of the Monkees, and Harry Saltzman, who made his bones with the Bond movies, it opened with a fair amount of fanfare, but then closed after a week when the principals realized they had a dog on their hands. It was immediately shelved, and it's been screened very seldom since. Rumors state that Kirschner won't have the film re-released during his lifetime. Meanwhile, a bootleg floats around in Japan. You can hear sound clips from the Toomorrow album here.
Even before Toomorrow, there was Funny Things Happen Down Under, which was Olivia's first feature back in 1965, when she was all of 17.