Apple, as you said, one of the best performances from Claude Rains is his role in Alfred Hitchcock's "Notorious" from 1946. A film also starring Cary Grant and Ingrid Bergman, Rains actually had to wear Cowboy boots in his scenes with the much taller Bergman - Rains wasn't terribly tall but one of the best character actors ever. He plays a Nazi supporter who's being sectretly infiltrated by Bergman, a spy, and Rains is able to make the character appealing and actually garner sympathy from the audience. Masterful acting and script in this Hitchcock masterpiece.
And I know Capo already mentioned Rita Hayworth in the 1946 film "Gilda", but I recently saw it for the first time during Summer Under the Stars and was floored by Hayworth's performance of "Put The Blame On Mame." Though it is actually the singing of Anita Ellis, Hayworth's slinky performance of the femme fatale is one of the more provocative moments in movie history.
"In keeping with the film character Gilda being "the ultimate femme fatale", the song sung by her at two scenes facetiously credits the amorous activities of a woman named "Mame" (the name evidently chosen to rhyme with "blame") as the true cause of three well-known cataclysmic events in American history: The Great Chicago Fire of 1871, Great Blizzard of 1888 in New York City and the 1906 San Francisco earthquake." - Wiki
The song is actually performed twice; the first an acoustic:
