There are indeed quite a few free Kindle books all the time. Some books are always free, some are free for a week or two as special promotions. Right on Amazon’s site, you can do that specific search: “kindle free books.”
Maybe half to three quarters is shlock, but there are some great gems, especially first books in long series that are now offered free with the hope that you’ll buy the rest.
You’ll also find packages of multiple books for sale cheaply during promotions, like 10 for 99 cents.
If your favorite author has facebook or an email list, get on it, because they will cross promote and tell you about the free specials.
If you like fantasy and sf, Baen has a free library: http://www.baenebooks.com/c-1-free-library.aspx
Anything in the public domain - basically before 1922 - can probably be found free for Kindle.
And then of course your library may also have titles for lending.
Kindle Unlimited has a free trial. I found it, well, limited, in that many of the books I wanted weren’t included. I decided that giving myself a $10 a month allowance for eBooks made me much happier, because I get to pick what I want and keep the books.
Don’t forget that nearly any Kindle title has a free sample that will let you read a few chapters before you buy. This is super helpful to me. If I get to the end of the sample and am still eager to read on, then I can buy it.
