What a Relief!
Tom Patterson, of the U.S. National Park Service, wrote a great paper five years ago on improved realism in NPS maps. There's some very insightful analysis that was useful even to a layman like me. He covers a variety of techniques that increase realism, such as aquafication, texture substitution, illuminated relief, outside land muting, and more. Plus, the illustrations are fantastic -- this terrific example from Crater Lake shows how technique at the Park Service has evolved in just a few years:
Also featured on his site is a great physical map of the lower 48 U.S. states.