If you're not familiar with the
Baen free library, it's a good place to start. You may recognize many of the authors, and the reviews on the individual book listings can help you sort out the other ones. The ebooks Baen sells are all in the $4-6 range, and they're available in several formats, including for the Kindle.
There aren't yet a lot of ebook review sites, and the book review sites are heavily skewed toward pop fantasy & paranormal romance right now.