Lucasarts has released concept art for Star Wars Episode III: The Revenge of the Sith. There are two images on their site as of today, one of a special elite clone trooper -- called a sky trooper -- that has a special jet pack. The other image is an ARC fighter, a special starship that seems to be a cross between an X-wing and the N1 fighter from Naboo or the Jedi Starfighter.
I've also discovered a few webmaster downloads that can be used on Star Wars fan pages and I plan to use them eventually. The first is listed below.