Farrah Fawcett: Charlie's Angels (animated GIF)
The infamous oops scene from "Angels in Chains" (S1 E4, originally aired 20 Oct 1976). Even if you constantly stared at her tits - and who didn't - you needed a quick eye and good VCR at the time to catch this.
Thanks to modern technology, here's one of the best downblouse views of the decade...