As mentioned, some of the best dios I've ever seen have been done by Bob Letterman. However, its not the sheer scale of his works that astounds me. All of them feature very fine details, superior to the Tiger dio posted above.
Noted, the dio is nice, but you gotta look at some other stuff that's available, there's much much better. Tamiya Model Magazine feature some really nice, sporadically however. Also, check out http://www.digitaldioramas.com/ (unfortunately, no longer running now) also had some good stuff, and the Armorama.com website, if you take the time to go through their posted works has some astounding stuff. Also the Missing-lynx website has some phenomenal stuff.
Check out this one, very imaginative:
http://www.network54.com/Forum/110741/message/1181767057/Herr+Hauptman%27s+Champagne