The Conversation is just a classic great movie. Gene Hackman plays a surveillance expert who gets too involved in a dangerous case. It is possibly one of the best performances by the perennially brilliant actor. But everything else about this tense thinking man's thriller is perfection too.
Francis Ford Coppola made this in between the first and second Godfather films, and for my money it is just as good–if not better. He deals with issues of privacy, intimacy, paranoia, and perception in his complex script with intelligence.
Honestly, if you haven't seen this movie, you haven't seen what these two exceptional men are capable of.