I got a Kindle as a gift this past Christmas, and I love it so much. After getting it set up and whatnot, I started looking through Amazon for books, and was so surprised at all the free books that are available at any given time!
To date, I have over 900 books downloaded, and I haven't paid for a single one! Granted, there are some that are just not that great, but after reading the first couple chapters and deciding that I'm not interested in a particular one, I just delete it and move on to the next. I do read the reviews for them, but because some people like them, does not necessarily mean that I will....so I download everything that looks remotely interesting at the time.
I stumbled upon a couple of great websites that I check daily for free books. The first one that I go to is Pixel of Ink. This site updates several times a day with links to Amazon for free and bargain books.
The next website I like to look at is I Crave Freebies. This site has a lot of different freebies, but if you click Books & Guides in the category menu, just the books are listed. This is usually updated at least once a week, sometimes every couple days, but when it is....there is a list sometimes of 100+ free books available at Amazon.
The third website I like is Free Kindle Books and Tips. This site is updated probably once a week, more or less with free downloads.
You can subscribe by email to all 3 of these websites, so when there are new books available you can be notified. I realize that any free books available at Amazon can be found by searching around their site, but I really enjoy the updates that these websites provide. I've gotten some really great books this way....and all for FREE!