Suvudu has started up a free library that gives away electronic editions of the first books in some popular series. If you haven’t read Noami Novik’s Temeraire series or Kim Stanley Robinson’s Mars series, check them out. I recently read the first three books in the Temeraire series and really enjoyed them. Think Patrick O’Brian with dragons. If you have a Kindle or Kindle for iPhone you can download them straight to your device for free.
Also, Tor is continuing to offer great books for free, this time giving away Charles de Lint’s Spiritwalk.