LibriVox - public domain audio books

LibriVox volunteers record chapters of books in the public domain and release the audio files on their website. Their goal is to make all public domain books available as free audio books and their catalogue includes complete books, short works, collections and poetry. The completed works are available for download in mp3 and Ogg Vorbis formats.

You may, of course, prefer to read your books. Project Gutenberg has about 20,000 free ebooks available in the public domain and, thankfully, a searchable database.