In this ten minute video created by Glyn Dewis, you'll get a nice little look at how to add sun rays to any photograph of your choosing by using gradients, layer masks and smart objects.
Polish photographer Boguslaw Strempel has a fantastic series of landscape photographs of mountains and valleys found in Poland and the Czech Republic. Strempel visits his photo spots early in the morning, when a blank of fog is hanging over the treetops. As the sun rises, the trees cast long shadows across the valley, turning the scene into a magical display of sunbeams.
Photographer Alexander Harding has a beautiful project titled "Visible Light" in which he turns light itself into the subject of photographs.