You can find lots of great photos on the Official Iditarod site. The Junior Iditarod is off and running right now. Awesome.
Despite common usage in annoying commericals or movies, mushers do not say "Mush" to their dogs. One theory as to how this term came to be, is that the French trappers were overheard saying "marche" to their dogs. The term to mush and musher stuck though, and are used to describe someone who runs sled dogs.
Mushers will say, Hike! or All Right! to get the dogs to pull, however, it's not generally needed. The dogs pretty much ALWAYS want to pull. I said, "Ready? All right!" to get my dogs attention and to start in unison.