All of these relate to iPhone:
The Photographers Ephemeris is absolutely fantastic but pricey (you can access it on your computer for free). Alternatively there is Sun Seeker which is similar but less expensive or free depending on the version you go for. These apps can be used for working out the sun and moon positions and related times.
I don't use it regularly but Longtime Exposure Calculator is a handy app to have if you are using ND filters. It will allow you to easily figure out the correct ND filter exposure time based on the exposure time without the filter and there is no need to do any maths.
Another app I've found quite useful is the Geotag Photos app. This simply logs your GPS position as you walk around taking shots and then it allows you to easily tag all of your photos with accurate GPS data during post processing - just make sure your phone and camera clocks are in-sync. It does impact the battery life of your mobile device but saves you from having to buy a separate GPS unit. Although it is about time Canon DSLRs had geo tagging functionality built in!
I'm sure you know already but Instagram is great fun for posting shots, it's just like Twitter for photographers and has a really active community. Giving your photos a faux-lomo look is entirely optional!
Lastly Nik Software's Snapseed is really quite powerful for photo editing directly on the handset, I've been really impressed with it. Their desktop software is very good and so is their mobile software. Although I realise from your question that you may not be so interested in this type of software.