Warcraft III mod, Defense of the Anicents, at Gamescom.
Defense of the Ancients 2 (DOTA2) is likely to debut at Gamescom due to a listing on the official expo site that shows Valve as an exhibitor set to show a product under the "strategy" category.
DOTA2 was announced over a year ago by Valve, but nothing from the game has been seen. DOTA creator Abdul 'Icefrog' Ismail had seince reassured the game's fans that the sequel wouldn't replace the original right away.
Since DOTA's release, derivative games such as Demigod and League of Legends have been released, while a cartoonish 2D platformer version, Awesomenauts, will be hitting Xbox 360 and PlayStation 3 consoles this year. Blizzard even released a free DOTA mod for StarCraft II at BlizzCon 2010 (though the mod hasn't been officially released to digital distribution yet.)
Gamescom runs from August 17-21 in Cologne, Germany.