I really liked
The Big Bus and
Cold Turkey. The latter actually has some cachet (Norman Lear's full length motion picure). The former is roundly considered to be awful; I think it's hysterical.
On a less ludicrous plane, I think that Douglas Trumbull's movie
Silent Running, starring Bruce Dern, is terrific. Trumbull was responsible for the special effects in Kubrick's
2001; and he does a great job with same in this early-1970's eco-scifi film.
Silent Running also introduces a literal forerunner of C3PO in its three droids, Huey, Duey, and Louie. Double-amputee actors provided many of the actions of the tiny droid costumes.
