Tombstone and Jeremiah Johnson have to be the most quotable movies.
I nominate The Outlaw Josey Wales as king of that hill. It's chock full of memorable quotes.
+1 Been binging a bit on some old Clint movies. Started with a couple Dirty Harry movies and am currently watching 'The Good, The Bad and the Ugly". Been a long time since I watched that one but so far its still a good one IMHO.