Just had this email from Amazon. If you have a book published with them via KDP you can now create discount deals to promote your book. It's free to do and can be a great way to get exposure for your book.

I know this won't apply to everyone but even if you don't have a book published with them it's still worth checking out the link I've posted as you can get decent deals on other ebooks.

The email I received is below:

Hello,

We are excited to introduce our newest KDP Select benefit – Kindle Countdown Deals. This is a new book promotion tool that lets you provide readers with time-bound promotional discounts for your Kindle books, available on Amazon.com and Amazon.co.uk.

Here are some of the benefits of Kindle Countdown Deals:

Set time-bound promotions – You control how long your book is discounted. The time remaining for your promotion will be visible for customers to help generate excitement for the price discount.
Customers get a great deal – Your customers will see the great deal they're getting with the regular price included on the book's detail page, right beside the promotional price.
Retain a 70% royalty rate – You will earn royalties based on your regular royalty rate and the promotional price. As a result, if you are using the 70% royalty option, you'll earn 70% even if the price is below $2.99.
Increase discoverability – Customers can easily browse live Kindle Countdown Deals at www.amazon.com/kindlecountdowndeals – a great way for you and your books to get discovered.
Monitor performance in real-time – A new KDP report displays sales and royalties at each price discount side-by-side with pre-promotion performance, so you can compare results.

Visit your KDP Bookshelf and click on "Manage Benefits" to get started.

Kind regards,
The Kindle Direct Publishing Team