Google Books is absolutely
not the "Grandfather" of free ebooks. That honor would go to Project Gutenberg. PG is not only older than Google and older than the Web, but it is older than Sergey Brin and Larry Page.
I don't consider a DRM-restricted book to be genuinely free no matter what the price -- it's like a physical book you're only allowed to read in your living room, and the covers seal shut if you try to read it in bed. That cuts out a fair percentage of "free" ebooks for me. I buy a fair number of non-DRM-restricted ebooks (thanks, Baen; how about I just hand over my wallet and get it over with?) but I will not accept a DRM-restricted book even at no charge.
My choices of
gratis and
libre ebook sources, in order of quality and preference, are as follows:
MobileRead (right here; best formatting)
ManyBooks (good formatting, and I like their site)
Feedbooks (marginally better formatting than PG)
Project Gutenberg (the
real granddaddy of free ebooks)
Munseys (bad, but they have some hard-to-find books)
The Internet Archive (useful for some primary sources for research)
Google Books doesn't even make it on there because most of their public domain books are nonetheless "preview only", and tend to be either PDFs of scans of the books or un-proofread OCRs of those scans. They're not too bad to read online, but as far as being usable on an ebook reading device, they're barely above worthless. The Internet Archive is also afflicted with bad scans and worse OCRs, but they have a lot of weird stuff like WWII-era government publications which, if you need 'em, you can't easily get anywhere else.
Incidentally, signing up with
Distributed Proofreading and proofreading a page or two a day is a good way to give back to the free ebook community. Plus it's fun.
Courtesy of Baen Books, a top SF publisher, I also get books from:
the
Baen Free Library
Fifth Imperium (downloadable images of Baen's free CDs)
Beware of Baen, by the way. They'll give you the first book or two in a series free, and the next thing you know, you'll have your shopping cart full of ebooks and be canceling your plans for the weekend. Insidious, that. A fair percentage of my high-priority TBR list came from Baen.