I have a droid phone, not an iphone, and these are some of the most used apps that I have ...I only download the free apps (except the weight watchers one)
game wise ~ it's words with friends and hanging with friends - scrabble & hang man with any of your facebook friends that play.
other apps ~ grocery iq .. someone already listed this..my husband and I can both add to the grocery list and it seperates them out into the aisle they go in, plus you can arrange the aisle according to the order they are at your favorite store.
the weather channel ~ just to check
sound hound ~ if I'm in the car and I hear a song that I want to add to my ipod play list, I can just touch it and it recognizes the song & keeps a history.
key ring ~ someone else mentioned it, too, some stores it doesn't scan, but at least the number is right there & they can type it in
I also use the calendar that came on my phone .. trying to input everything into it so that if I don't have my little calendar I can still know what I'm doing if someone asks or I need to plan something.
I use the navigator sometimes too if I'm going someplace I haven't been before.
If you do weight watchers at all, there's an app that not only will calculate your points, but will keep the diary and can find the points ~ ultimate weight watchers diary.
I like I heart radio or Pandora ~ both free, unlimited hours, play radio stations...good when you're out somewhere and want some music.
Amazon kindle ~ syncs with my regular kindle, so if I want to read & I don't have my kindle with me, I can still catch up.
If you have small children, norad santa tracker has an app this year ~ right now it just has some games (tic tac toe, brick drop, etc), but Christmas Eve it will track Santa :) if you want, you can track him on your computer for the kids...it's great! shows where he is going next, some info on the places where he is, starts in the afternoon or evening sometime on the other side of the world, very cute! we don't have any small children at home anymore, but we keep it up just to watch!
don't forget the program monitor...or if your phone doesn't have one, get app killer...you can shut off any apps that you're not using right then but are still open and it saves your battery power.
have fun!
D.