From 2K Greg's announcement:
The first is Civilization and Scenario Pack: Korea, which allows you to play as Sejong, King of the Choson Dynasty as the leader of the Korean civilization. The scenario begins with Toyotomi Hideyoshi having just unified Japan, and is looking towards Korea to expand his empire. In the scenario you can play as Korea, China, Manchuria, or Japan.
The second is something a bit different than we’ve done in the past: Wonders of the Ancient World Scenario Pack. This add-on adds three new early-game wonders to the game: The Mausoleum of Halicarnassus, the Statue of Zeus, and the Temple of Artemis. The scenario is a race between the civilizations to be the greatest builder of the Wonders of the Ancient World.
The second is something a bit different than we’ve done in the past: Wonders of the Ancient World Scenario Pack. This add-on adds three new early-game wonders to the game: The Mausoleum of Halicarnassus, the Statue of Zeus, and the Temple of Artemis. The scenario is a race between the civilizations to be the greatest builder of the Wonders of the Ancient World.

There are some popular requests in here that I bet will make some of you very happy.
And so without further ado:
Modding Addendum
The DLL source code will be released with the fall patch, allowing modders to compile modified DLLs for their Civilization V mods.
BUG FIXES
General
Mod Browser - The "Get Mods" button is now hidden if the user has disabled the steam overlay.
...
Mike