In the lord of the rings the way they made the battle of Pelenor Fields was quite amazing. they actually combined several different layers of filming, the background filming, the horse charge, the cgi elephants, and the lighting and animation layers, mostly animated at the WETA digital workshop.
Shelob is another example of WETA digital's work.
Also the way they animated the mass horse charges was cool. watch it here: http://www.youtube.com/watch?v=x2FimkptxIk&feature=share&list=PLA74A60F2F8D701A3