One of the smartest science fiction movies of the atomic age is pretty stagey, but the proto-Philip K. Dick story is engrossing, the minimal sets and saturated lighting are lovely, the musical score creeps up your spine, and there's that guy from Plan Nine from Outer Space. Make sure to see this one, preferably on DVD and a big screen.
Cronenberg's first feature film, Shivers (a.k.a. They Came from Within) defines his entire oeuvre immediately. It manages to simultaneously be exploitive, deeply horrific, and very intelligent, a perfect film for the mid-70's zeitgeist of sexual liberation and modernized living.
Out of print on home video since the 90's (used DVDs are currently selling on Amazon for over $100), so see it before it disappears.