Since I’ve been talking about free things a bit today I figured I’d mention that “The Purloined Letter” is free over at Project Gutenberg in both text and audio versions. There is also a crapload of free public domain books there other than the Poe stuff. Project Gutenberg has a handy “Bookshelf” feature that groups books by subject or genre. For examle the Science Fiction, Fantasy, and Folklore shelves are certainly worth a look.
Though not as simple in its formats you might also try the Million Book Project. Most titles are more of a scholarly bent, and span a more dynamic linguistic range, but worth a look none-the-less. You’ll need LizardTech’s djvu plugin (PDF’s cooler, slightly aloof younger brother).