At the start of each month, the fine folks over at SF Signal compile an awesome list of science fiction, fantasy, and horror (and thereabouts) books coming out in the next month. Here are the Steampunk (and related) books from their lists for December, but please look at the full list too if you are looking for something outside of our little fiefdom.

The Bookman Histories by Lavie Tidhar
The Bookman Histories by Lavie Tidhar, Angry Robot, December 26 (Omnibus of The Bookman, Camera Obscura, and The Great Game.)
The Doctor and the Rough Rider by Mike Resnick
The Doctor and the Rough Rider by Mike Resnick, Pyr, December 4
Doktor Glass by Thomas Brennan
Doktor Glass by Thomas Brennan, Ace, December 31

Fungi Anthology
Fungi edited by Silvia Moreno-Garcia and Orrin Grey, Innsmouth Free Press, December 1 (Not Steampunk per se, but contains works by Steampunk writers Jeff VanderMeer and Lavie Tidhar.)
Gilded by Karina Cooper
Gilded: The St. Croix Chronicles by Karina Cooper, Avon, December 26
The League of Illusion: Legacy by Vivi Anna
The League of Illusion: Legacy by Vivi Anna, Carina Press, December 31
Nell Gwynne's On Land and At Sea
Nell Gwynne’s On Land and At Sea by Kage Baker and Kathleen Bartholomew, Subterranean, December 31
The Steam Mole by Dave Freer
The Steam Mole by Dave Freer, Pyr, December 4
Touch of Steel: A Novel of the Clockwork Agents by Kate Cross
Touch of Steel: A Novel of the Clockwork Agents by Kate Cross, Signet, December 4