The Elder Scrolls V: Skyrim - Dragonborn DLC Available for Pre-order on Steam

As far as I'm aware it's not very common to make a DLC available for pre-order, but that's what is happening on Steam with Dragonborn, the latest DLC for Skyrim which has been released only on Xbox 360 so far.

As with the other story-heavy DLC, Dawnguard, Dragonborn costs $19.99/€19.99. Here's what it includes:
With this official add-on for The Elder Scrolls V: Skyrim, journey off the coast of Morrowind, to the island of Solstheim. Encounter new towns, dungeons, and quests, as you traverse the ash wastes and glacial valleys of this new land. Become more powerful with shouts that bend the will of your enemies and even tame dragons. Your fate, and the fate of Solstheim, hangs in the balance as you face off against your deadliest adversary the first Dragonborn.