This tower defence style game is out now. It is available on Xbox 360, PlayStation 3 and PC. If you buy it on PC and on Steam you can get exclusive items, The Aperture Science Handheld Portal Device and Four Team Fortress 2 Familiars. Also the Steam version has lots more achievements than the console versions if you are in to that type of thing.
From what I seen it looks good and a lot better than Orcs Must Die! for one thing it has multiplayer and team work is encouraged while Orcs Must Die! only had single player, what were Robot Entertainment thinking?
You should get the Steam version of Dungeon Defenders where you can also save 10% of the main price. Other stores are also available.