OneLug. It is over 7 feet high and its base, which contains 25 ents and 100 orcs, has a diameter of 8 feet. It was revealed in November, 2011 at the BrickCon in Seattle. It will only be on display at one other place: TheOneRing.net's 'An Unexpected Art show.'
If you click on the picture you can see a much larger version, and it is amazing. It is astoundingly accurate to the scene in The Two Towers, featuring Treebeard, an ent on fire, and water flooding Isengard. You can even see Saruman watching from his balcony. The tower was directly inspired by artwork by Alan Lee, and seems to follow it to a brick. Great job, OneLug!