I haven't had the time to check out all 44 of these sites yet but I know for a fact that several of the sites are great for ebooks and audio books. Most of the books on offer for free are classics and other books whose copyrights have long expired, but there are also sites that feature the work of new writers who see trading their early work for some exposure and word-of-mouth advertising as a positive thing for their careers.
Friedbeef's Tech has the Best Places to Get Free Books - the Ultimate Guide, a listing, with links, of the 44 sites. You might have some fun with this one. My favorites include Wowio which offers full version ebooks on just about every topic imaginable, ManyBooks which is a great spot to download the classics in ebook format, and Podiobooks which makes available audio books from new writers looking to spread the word about themselves.
But that's only 3 of the 44 that are listed, and I've only visited the sites of about a dozen of them so far. So if you find something that you really like, please leave me a heads-up in the comments section.