Over the past year, there's been a huge movement towards free online books and other learning materials. One distributor, WOWIO, has already seen some success in offering free books. Here's how they describe themselves:

"WOWIO is a new kind of online bookstore that enables readers to download ebooks for free, using commercial sponsorships to compensate authors and publishers. Readers get free ebooks. Sponsors get a powerful new channel to communicate their message to precisely the people they want to reach. Publishers get a new means of distributing their books, expanding their readership, and monetizing their intellectual property."

On the upside: WOWIO users can instantly download free books, many of which are not in the public domain. However, WOWIO does rely on sponsors to fund these publication, which means you'll have to put up with some level of advertising. On the whole, this looks like a successful business model which in the future could work for academic authors.