Sorry, I have an Android phone, so it might not transfer to iPhone...... Everyone has listed great apps, here are a couple that weren't mentioned yet and some are a little broader use than you asked:
Gas Buddy, to find "local" gas prices and gas stations, even as you travel - priceless
Square and the attachment - when you sell things at your garage sale, you can take credit card payments, people sign your phone with their finger, and it goes into your bank account, slick.
Tune In Radio (free) - to listen to your favorite radio station from just about any city, NPR (car talk, lol!)
Ebay App to keep up with your bids
Timer - just a big digital count down or up timer