Audible.com. More than 20,000 hours of audiobooks, audio newspapers and magazines, for PC or mobile device playback. Daily audio digest of The Wall Street Journal, New York Times, San Jose Mercury News, The Economist magazine, and Forbes. The site also features a collection of audiobooks from best-selling authors, on-demand radio (including Marketplace, Nightly Business Report, Fresh Air, Car Talk), and speeches, lectures, and language learning.

AudioFile. The site for the publisher of AudioFile magazine, which also publishes the annual Audiobook Reference Guide, an industry directory of suppliers, wholesalers, distributors, and others.

Audio Publishers Association (APA) has more than 190 members and issues the most comprehensive reports about the industry (though the full report costs $1495 to non-members). The site is a good source of information about audio publishing.

Books on Tape, founded in 1975, claims to have "originated the concept of recording full length readings of great bestsellers for rent through the mail." The site offers a large selection and some audio samples.

MediaBay. MediaBay owns Audio Book Club, the first book club devoted solely to audiobooks; it has also recently acquired a slew of other audio book clubs, making it "the world's largest marketer of audiobooks through the Internet and direct mail." Through its other subsidiaries, RadioSpirits.com and VideoYesteryear.com, MediaBay produces, broadcasts, syndicates, sells, and licenses popular old-time radio and classic video programs, including vintage comedy, mystery, detective, adventure, and suspense programs.

MP3Handbook FAQ. A useful FAQ about digital audio file formats.

Recorded Books. One of the first audiobook publishers to offer unabridged readings. Their site allows users to rent or buy books on cassette.

Secure Digital Music Initiative (SDMI) FAQ. Alarmed by the explosion of unauthorized MP3 music files on the Internet, the Recording Industry Association of America (RIAA) pushed for the establishment of a body to recommend standards for the secure, copyright-protected, digital distribution of music. This PDF document, published in September 1999, answers questions about the SDMI's mission and activities.

Words on Tape: How to Create Profitable Spoken Word Audio on Cassettes and CDs, by Judy Byers, takes readers through the process of conceiving, recording, and selling audio tapes step by step, in great detail, and with plenty of anecdotes. Self-published in 1997 by a veteran producer and consultant, this is the most complete how-to guide available.