Now this is cool: Andy Serkis (Gollum in The Lord of the Rings films) stars in an audio performance of The Screwtape Letters by C. S. Lewis, produced by Focus on the Family. Judging from the video link, Serkis sure does a good evil-genius howl.
Years ago, John Cleese recorded a very good Screwtape. Also, fans of the Lewis book should check out the stage version by the FPA Theatre Company.