I think the best quote of all from that film is 'I'm not left-handed either'. It comes at the end of a fantastic sword-fighting sequence when the great swordsman Inigo Montaya, who often fights with his left hand because otherwise he will win too easily and get bored, finds himself almost beaten by a mysterious man in black (fighting left-handed). Inigo laughs, explaining that he isn't actually left-handed, changes back to his right hand and now expects to win easily. Then the mystery man laughs and says that he isn't left-handed either...changes to the right hand and beats Inigo. This is a great scene in both the book and the film.
Prince Humperdinck also has great lines, especially when he complains that he is so busy because he has a wedding to arrange and a wife to murder, among other chores.
You can find other good quotes from The Princess Bride here.