The one mentioned WAY above about bikers and Vietnam is actually (IIRC) about bikers and Cambodia -- THE SAVAGE SEVEN. Theme song, "Anyone For Tennis?"

To return to the original theme of counterculture films:

ME, NATALIE
The unattractive Patty Duke (rejected early in the film in a cameo by the unknown Al Pacino) gets on her motor scooter and leaves Brooklyn for Greenwich Village.

THE MAGIC GARDEN OF STANLEY SWEETHEART
In which young Columbia student Don Johnson is seduced by a very young, very ample, very naked Holly Near.

GETTING STRAIGHT
Elliot Gould desperately attempts to get his masters degree as his car, his life and the campus disintegrate around him. I loved it.