Craig Mullins, one of the best artist i have ever seen, has done concept art for Halo 2 and i have seen some never before seen concept arts for the game. Also he has been doing some concept art for a new Bungie game. I don't know if those are for a cancelled proyect but it looks very interesting. According to each art, it looks like he has done them during September, 2004.

Here is the link. Go to commercial work and scroll down till you see Bungie.
http://www.goodbrush.com/mainpage/index2.htm

Here are some pics:
http://www.goodbrush.com/cm/albums/commercial_projects/bungie/crashed_phor.jpg

http://www.goodbrush.com/cm/albums/commercial_projects/bungie/marine-and-compy.jpg