Yesterday, thanks to a post on Dear Author here, I signed up for Tor's newsletter.
If you sign up for the newsletter, you'll receive a free e-book every week.
According to the Tor Publishing site, "Our next free book is Old Man's War by John Scalzi, 2006's winner of the John W. Campbell Award for Best New Writer. Next week, Through Wolf's Eyes by Jane Lindskold."
So, go here and sign up for the newsletter.