Besides tha basics I use Weather apps a lot - especially the radar. Living in Tornado Alley we have some nasty storms and I'll follow them on radar.
On the Medical side I have Glucose Buddy, BP
Buddy, an ICE program, Walgreens (For some Rx refills) and OsiriX
For Travel I have AA
, Flight Aware and I recently added "Visit Dublin"
I don't ready books on the iPhone, but I keep Pocketpedia on it to avoid buying books twice - a bad habit when the books hit the Bargain Section at B&N.
The rest of the stuff is for the grandkids.