There are a number of quotes in Star Trek VI: The Undiscovered Country that are from Shakespeare plays. The title is one, and is cited on screen:
Chancellor Gorkon: I give you a toast: the undiscovered country. [The others look confused] The future.
Everyone: [Raises glasses] The undiscovered country.
Spock: Hamlet: Act Three, Scene One.
Gorkon: You have not experienced Shakespeare until you have read him in the original Klingon.
There are many other Shakespeare quotes in the film, mostly from General Chang. What plays are they from?