Three Days of the Condor, what a piece of shit. Redford does some interesting early films of which Three Days is the best. Other overlooked gems include include the wry The Candidate with its great ending line and the well made Downhill Racer (directed by Michael Ritchie of all people.)
For extra credit, without looking it up, answer this question. Who was his character in his only Twilight Zone appearance, in the episode Nothing in the Dark?