These eight are from Random House and are the same ones being offered by Stanza for the iPhone. In addition, the Charlie Huston books have been made available, one at a time, in PDF format over the last few months:
Free-Range Chickens by Simon Rich
The Foreign Correspondent by Alan Furst
Caught Stealing by Charlie Huston
A Dangerous Man by Charlie Huston
Six Bad Things by Charlie Huston
Murder List by Julie Garwood
The Idiot Girl and the Flaming Tantrum of Deathby Laurie Notaro
The Whiskey Rebels by David Liss
The odd one out is from Samhain Publishing. Be warned, it has a content warning and is for an adult audience:
Love Me, Still by Maya Banks
Update: Another book has been added as a freebie today:
Prague by Arthur Phillips