I know I have done a post like this before, but this time I won't focus on how and what but more on the where of cheap/free ebooks.
Two posts I have done in the past are
Ideas on cheaper reading (6 April 2011)
Manga and FanFiction (29 May 2011)
They are still accurate and interesting so I won't be talking about stuff I have talked on in those, this time I will focus on how I find cheap readings from sources that not everybody has possibly found.
Some of these links are to websites that fully focus on Kindle content, even if you don't have a Kindle you can use most of these with the free Kindle app for your phone/pad/computer (UK/US). With others you can choose the format yourself.
I start with two that are the closest to the actual writers themselves:
Follow the blog, twitter or facebook (preferably all 3 of them) of a writer you like and possibly other writers that write in the same genre. Often writers will announce when their book goes free for a while on Amazon, B&N or Smashwords. Even if you don't plan on reading these books at that exact moment, if they interest you pick up a copy as this might be the only chance you have to pick it up for free. I have picked up quite a lot of books from writers I like this way.
The next option is to become part of a group like eBook giveaways on Goodreads. These are places where writers can post links for when their books will go free for a while. You might not know these writers or their work but you might find that after picking up a copy you do really like it.
For both these sources I would say that leaving a review after you finished a book is not much to ask when you got it for free, is it?
The next ones are slightly less involved with the actual writers, but great places to pick up books:
For easy browsing you can use Smashwords where people have put their own book online. You can choose your own genre and then press "Free ebooks" and it will only give you the ones that are free, listed from the most recent added to the oldest. They also sometimes have promotions where they offer a whole list of books for free or reduced price, they had a huge one over summer and I expect they might do one again over winter.
Subscribe to book bloggers, some of them might make a deal with a writer they blog about and offer the book they write on for free for a short period of time, always nice to get a hold of, especially if they blog about a genre you like to read in and they might spark some interest in writers you didn't know yet. Alchemy of Scrawl made a blogpost about book bloggers listing quite a vast amount of them here.
These last ones are further away from the writers themselves:
Both Project Gutenberg and Many Books offer books that are older, usually they have run out of copyright. If you know what you want I would go for Project Gutenberg but if you like to browse I'd go with Many Books they both offer quite a vast amount of books though they might not all be available at both places. Try it, I have found some interesting books for my uni course there and also just old books that I come across that sound interesting.
The last thing I would like to mention are the lists of free Kindle books that get updated once in a while. These are UK resources only. Kindle users forum updates it's list every day at 9 in the morning though they don't always have new books and I also follow Kinworm who apart from doing blog posts with a lot of information on the kindle also lists new free books when they are available. I use both of these sources quite a lot and amongst others have found a couple of best-sellers that were free for a short amount of days.
This is it for now! Have fun reading!