If you're happy to sell your soul to Amazon, or you're not bothered about them not paying the tax that they should, you're going to want to know about the books you can get for free or for a small sum of money to read on your Kindle or Kindle app device. If that's the case, you might want to try BookDip which says of itself "Daily Deals on Bestselling Kindle eBooks from Big Name Authors" Basically you just sign up and tell them what sort of category of books you're interested in, and then they send you a daily email with hand picked free or heavily discounted titles. They only send information on books by wel known authors and/or which have got very positive reviews. I'm not entirely sure how they work that out, or what their criteria is, so you may find that they're bang on the money for you or totally off the wall.
Alternatively, if you don't fancy BookDip, try Book Gorilla which does something very similar. This one says of itself "BookGorilla sends you a single daily email alert with the best deals on books that match your reading preferences, including bestsellers and freebies!" I've tried this one, but not BookDip, and it does send an email a day. The only problem that I have with this is that you do tend to glaze over very quickly; I only have a couple of categories chosen, and they send huge numbers of suggestions every day, though to be fair, you can limit to 12, 25 or 50 - I've set a limit of 25, but it seems so many more! However, you can of course unsubscribe whenever you like.
I do know that there are more services than this - these are just a couple that I've discovered recently - if you have others that you know, or want to suggest your own, please add details in the comments.