AFAIK, Amazon hasn't banned such sites, Amazon will just stop paying click-thru affiliate fees to sites that emphasize free Amazon ebooks, per:
Amazon tightens affliate fees on Kindle books Amazon to Change Free eBook Policy for AssociatesAnother concern (which I have not confirmed) is that with the Kindle Fire, Amazon has made it difficult (not impossible, but tedious) to read non-Amazon ebooks:
Kindle Fire Revew Some 29,000 free public domain ebooks in practically any format are available at
Manybooks.net which is basically a "convenience" indexing and reformatting engine of the ~42,000 book collection of
Project Gutenberg and they say that there are over 100,000 books available through the sites they list as
Project Gutenberg Affiliates Note that the books at Project Gutenberg are two-pass human proofread after the original book was scanned.
If you are okay with a fair amount of OCR errors, or willing to read books in .pdf (scanned) format rather than ePub, there are quite a few public domain books available at Google Books.
As a topical example of such a Google Book, this book with tips on making campfires can be downloaded in either ePub or .pdf form from the "gear" icon dropdown menu at top right:
The Art of Travel, or, Shifts and contrivances available in wild countries Update: This site seems to have a fairly comprehensive list of places to get free Kindle ebooks:
97 Places for Free Kindle Books Online (legally)