During my travels around the Internet and various forums I've came across a few sites that provide access to Free ebooks, so I decided to start consolidating everything that I found here, partly for my own reference but also because I thought that it may be useful as well.
If you know of any sites that aren't listed here, then please let me know.
Free Books Available on Amazon
These are all Kindle formatted, so all you need to do is just download them.
NB: Some books may not be free in your region, so be sure to check before you download.
http://amazon.com/freebookcollections
Free books or books which are temporarily free for s short time (Not classics)
Top 100 Bestsellers - Contains two lists, Top 100 Paid and Top 100 Free ebooks
Project Gutenberg
Many public domain books are available here in a variety of formats, including a lot of ereaders such as the Kindle, well worth browsing through.
ManyBooks
A lot of free books here, in an easy to navigate or search site
http://manybooks.net/
Smashwords
Lots of free ebooks available here but they also give you an opportunity to publish an ebook of your own as well.
http://www.smashwords.com/
Focused mainly on search to allow you to find free ebooks on other sites, pretty useful
www.inkmesh.com
Wonderful forums and a wiki that contain all sorts of information for all ereader devices, not limited to just the Kindle. Definitely worth checking for the forums as well as the ebooks.
www.mobileread.com
EReaderIQ
Find ebooks, find free ebooks and receive notifications when something that you're following becomes free or the price is reduced.
www.ereaderiq.com
This site actually lists books that usually require payment but as the title suggests, at bargain prices, well worth looking at.
www.dailycheapreads.com
Feedbooks
Free books and paid books but all very nice presented and available for download in a variety of formats.
BooksOnTheKnob
Another good site for ebooks!