There are some interesting websites to look at, going beyond Amazon. You can find different independent writers on these sites and some of the writing is really quite good:
http://www.getfreeebooks.com/
http://www.ebooksjustpublished.com/
http://finding-free-ebooks.blogspot.com/
http://www.free-online-novels.com/
For many of these sites, you won't get it in Kindle format, but Kindle reads mobi/.prc format. Some of these sites offer books that are in .prc; to expand your ability to get content, you should download Mobipocket Creator, which helps you convert .pdf files into .prc files you can read on your Kindle. Creator will create the books on your desktop and you can use the USB cable to load manually on to your Kindle.
Not all on books on these sites are free; some are offered for a nominal price, but you'll find what you want browsing through these sites. :-)