It's starting out with Naomi Novik's "His Majesty's Dragon," Kim Stanley Robinson's "Red Mars," Robin Hobb's "Assassin's Apprentice," Harry Turtledove's "Return Engagements," and T.A. Pratt's "Blood Engines."
I've read the first three of those and liked them. Can't really say anything about the other two.
I was also quite happy to find today that Audible has finally gotten around to adding the Honor Harrington series to its selection, or at least the first four books so far. Presumably more will be following later. Not free, but still awesome :)