THE BLACK CAT (Edgar Ulmer, 1934)
FRANKENSTEIN (James Whale, 1931)
BRIDE OF FRANKENSTEIN (James Whale, 1935)
THE MUMMY (Karl Freund, 1932)
THE BODY SNATCHER (Robert Wise, 1945)
BEDLAM (Mark Robson, 1946)
CORRIDORS OF BLOOD (Robert Day, 1958)
THE WALKING DEAD (Michael Curtiz, 1936)
THE MASK OF FU MANCHU (Charles Brabin, 1932)
THE BLACK ROOM (Roy William Neill, 1935)
ISLE OF THE DEAD (Mark Robson, 1945)
BLACK SABBATH (Mario Bava, 1963)
TARGETS (Peter Bogdanovich, 1968)
If you're interested in reading about Karloff's life and career, you would be hard pressed to do any better than the books of Gregory William Mank such as BELA LUGOSI AND BORIS KARLOFF: THE EXPANDED STORY OF A HAUNTING COLLABORATION and IT'S ALIVE: THE CLASSIC CINEMA SAGA OF FRANKENSTEIN.
And as an added Halloween treat, here's Karloff performing in an adaptation of Edgar Allan Poe's "The Telltale Heart" on a 1941 episode of the radio show INNER SANCTUM....