For me, the purpose of an app is to expand the uses of the iPhone, making it much more convenient.  Here are some great apps, some of which you may already be enjoying.  The first one is not free, but it may be well worth the hefty price of $9.99.  It's 1password  This app will put an end to your having to enter and re-enter usernames and passwords.  This securely stores all of them, and you can even have it automatically log you into a website with just a single tap.

Ever get a tune or song lyrics stuck in your head, but you just can't remeber what song they came from?  Well the free app called SoundHound will come to your rescue.  Just hum the tune or say the lyrics into the phone, and this app will tell you the title and artist of the song.  

Yelp is another free app that's worth downloading.   It's tailored to the iPhone and will guide you to the mechanic or shoe store you are looking for.  It lists reviews and locations.

And one more free app to consider is Flock.   With is app, you can automatically share photos with Facebook friends based on your shared location.  You'll never miss a photo that someone else took.   Just some suggestions to help you get the most from that iPhone.