There are a LOT of books available for free and they are sorted by retailer, so not just limited to Amazon only KU books.
I've got a huge archive
but still managed to find 10 books that I wanted. It takes awhile to get through the list but it's definitely worth it. Some of them will remain on sale for a few days, so even if you don't get to it today 6/24) you should still check it out.