How do you find the best light for photographing a building or waterfall or other site? I have three iPhone apps I can recommend: LightTrac, Golden Hour, and Sun Surveyor. These apps can help you figure out the best light for a given location on a given day. LightTrac shows you the direction of the sunlight overlaid on a satellite view of the place you want to shoot. It gives you the angle above the ground as well, so you can tell when the sun will rise above a building that may be across the street from one you want to shoot.
The app Golden Hour gives you the times of sunrise, sunset, golden hour, and blue hour – it can help you decide when to go to get that magic blue sky. Sun Surveyor gives you augmented reality projections over a live camera view and a map with street view, as well as providing information about the position of moon and the Milky Way, which is great for night shots.
I use these apps not only for photo shoots for clients, but also for trips abroad such as my trip to Italy last year, so I could take light into account in planning my itinerary (weather permitting of course).