Apps I find myself using a ton are: Youtube, Wikipedia, Yahoo Finance, Podcasts, Vine, Facebook, Liberty Mutual (My proof of insurance), iTunes U., Starbucks, Flashlight.
I just got my iphone a month ago (it's my first smartphone) and I'm freaking addicted to the thing. A year ago I was just another Apple hater but an iPad Mini and iPhone later I'm a fanboy lol.