The Devil and Daniel Webster /
All That Money Can Buy is my personal favored film featuring the devil as a prominent character. One of my favorite characters came out of Walter Huston's portrayal of the devil. It was later remade with Anthony Hopkins, Alec Baldwin, and Jennifer Love Hewitt as the devil. I haven't seen the remake, but I haven't heard any good things about it.
And even with my love for The Devil and Daniel Webster and my praise for Huston's performance, I think the best performance anyone has given as the devil is Robert De Niro with a mere special appearance in
Angel Heart, which (even excluding De Niro) is also a damn fine horror/Satan flick. De Niro's character was named
Louis Cypher, clever eh?
Polanski made his mark in the "Satan" category (if you can call that a category) with
Rosemary's Baby and later with
The Ninth Gate, both pretty fine films well worth the watch. Many consider Rosemary's Baby to be one of the greatest horror films ever made, and while I don't appreciate the flick that much, I can certainly understand the praise for it. It should be essential viewing for those who find interest in films about Satan (not that I'm a Satanist).
EDIT:
You should also check out
Faust (the silent version, I've been told to steer clear of the one released in 2000) and
The Omen.