Fit me for a dunce cap I've done it again. While searching Librivox for Holmsian goodies I stupidly searched just for dear old Sherlock and not ACD. If I'd been half as clever as I'd like my children to think I am I would have noted that in addition to The Adventures of Sherlock Holmes Collection Librivox's tireless volunteers had also recorded both The Sign of Four and The Hound of the Baskervilles. A couple of short stories can also be found in short story collections. (The Dying Detective, The Speckled Band and The Dying Detective again)
Fan's of Conan Doyle's other works will be pleased to find The Lost World, The Parasite and The Japanned Box also ready to be downloaded. Still in the recording phase are A Study in Scarlet and Tales of Terror and Mystery.