Some indie SciFi authors have teamed up to create a website called Discover Sci-Fi. Right now if you sign up for their newsletter you can get a free book from a selection of titles.
http://discoverscifi.com/
List of books...
Breakthrough - Michael C. Grumley
Better World - Autumn Kalquist
Extinction Horizon - Nicholas Sansbury Smith
Marines - Jay Allan
The Future Chronicles - Anthology/various authors
Warship - Joshua Dalzelle
The Terran Gambit - Endi Webb
On Silver Wings - Evan Currie
EDIT: I just got an email from them and it says click to get your free book
s so apparently you can get all of them free if you wish. I checked and was able to download a second book.