To me, sunrise and sunset are the two greatest times of day.  I have to say that I enjoy sunsets a little more, since they come at a more convenient time of day, but a sunrise can be much more satisfying when you're the only one awake to see it.

These photos are available in other places on the site, but I have consolidated some of my favorite scenes here.
 
 

Sunrise at North Window Arch Arches National Park, Utah	Sunset at Delicate Arch Arches National Park, Utah	Sunrise on the Dripping Springs trail Organ Pipe National Monument, Arizona
Sunset Saguaro National Park, Arizona	Sunrise at Cochise Head Chiricahua National Monument, Arizona	Sunset near Mount Lemmon Tucson, Arizona
Sunrise at Tellico Gap Cherokee National Forest,Tennessee	Sunset near Seljalandsfoss Iceland	Sunset at the Very Large Array Socorro, New Mexico
Sunset at Signal Hill Saguaro National Park, Arizona	Sunset Zion National Park, Utah	Sunset from the Olympic Village Atlanta, Georgia
Sunset over Prague Castle	Sunset at Brandenburger Tor	Sunrise at the Sierra Vista balloon rally
Sunset at the Rockland Hotel Sasco, Arizona	Sunrise in Afghanistan	Sunset in Afghanistan
Sunrise in Kuwait	Sunset in Kuwait	Sunset in Kuwait