BookGorilla allow you to choose the genres you like to read, then send you an email every day with Kindle books that are free or discounted on Amazon that day.
This is good, but I wanted more!
A couple of months I discovered that authors and publishers will give you copies of their books if you offer to review them! Sites like NetGalley and Eidelweiss allow you to sign up and request books that you would like to read. If the publisher approves your request, you can download a prerelease copy of the book. Then you post your review and send them the link.
This LINK has even more sites that allow you to request books in exchange for reviews. It also has other ways to read for free!