I will add a few apps that I find to be very useful.
Torch
Starmap
Met office
Redlaser (this is a price comparison app that works using bar codes, and saves me a fortune)
Memory-map
Decibel
Documents 2
Ebay
TrafficEye (allows you to see the display from motorway traffic cameras all over the UK)
TankScope (very amusing)
Wikihood
Tunein Radio
eCompass
Plus a selection of bird, tree and fungi guides for outdoor use.
Edited to add: I use a military grade (whatever that is) scratch proof cover on my iphone, and this is VERY effective, as well as being an anti glare cover at the same time. I use a rubber case to protect the phone in daily use, but will switch to an Otterbox armoured case when backpacking etc.