I don't know how many of you regularly check the Luminous Landscape site, but there's an article there by Kevin Raber that alerted me to this iOS app for landscape photographers called PhotoPills, and I've had the chance to play with it and am VERY impressed with it.
If you've used apps like The Photographer's Ephemeris or LightTrac, you may be familiar with their ability to predict the position of the sun and moon in different locations, and determine how the natural lighting will be on a certain date and time. There are other apps that will help you calculate depth of field, field of view, etc. Well, PhotoPills does all of these things, and much more, and does them better than any other app I've ever tried. I had seven photography reference apps on my phone, and this one app has replaced them all.
It has too many features for me to list here, but the two that rise to the top for me are the ability to easily plan a photography trip to a distant location based on when the lighting will be optimal, and a nifty tool that uses the phone's camera to display an overlay on the screen of where and when the sun and moon will transit the sky.
Right now it's an iPhone-only app, though an iPad app is coming and will be free. I could find no word from the developers about an Android or WP version.
My only two criticisms of it are 1) it's pretty complex. I wasn't be able to master it without watching the online tutorials, several of them twice, and 2) those comprehensive tutorials are narrated by one of the Spanish developers, whose thick accent can be difficult to understand at times, even for someone like me, who married into a family of native Spanish speakers.
Oh, and at US$9.99 it's not cheap for a photo reference app. But this is the sort of app that makes that sum seem like an incredible bargain. If you're a landscape shooter like me (I don't think portrait, macro, or street shooters would find much value in it), it's an amazing tool to have in your pocket.