The folks at Poynter had a nice Twitter chat on using mobile devices for reporting. A lot of it was about radio and how many pro reporters are doing most of their work on an iPhone or Droid device. The transcript is here:
But what you really want is this link, to the latest version of the Mobile Reporting Guide, from UC Berkeley:
You can get it as an iPhone or iPad app, but its also downloadable as a PDF, for free.
The Guide includes the pros and cons of apps you need as well as reviews of gear to extend the capabilities of your smartphone.