A few in no particular order:

Witness: for the story, and the visual poetry of a lot of the photography.

Alice's Restaurant: When it came out, I was living surrounded by a lot of the same
                noble patriots who beat the crap out of Arlo early in the movie for
                looking different. I cussed them out aloud in the theater, which
                wasn't especially mature or constructive, but It just got to me that
                deeply.

The Man Who Shot Liberty Valence: The one movie I have watched the most times.
                 John Wayne, James Stewart, and Lee Marvin, all in top form, put
                           together with John Fords' feel for the mythology of the old west;
                   works for me.

Cat Ballou: Mainly because I don't think I've ever seen an individual performance
                more hilarious than Lee Marvin as Kid Shaleen.

Young Frankenstein, and Monty Python and the Holy Grail, just because sometimes
                I like to laugh myself sick.

More recently, The Piano Player; I hadn't realized until the ending notes that it was a
                true story; a wonderfully done portrayal of a man surviving thru total
                hell.