Here is a very cool app. If you have Carbonite backup on your computer you can download the carbonite app from the apps store for free and log in and access any file on your home computer that has already been backup up to Carbonite from anywhere. You can download music and play it, pictures and any document it seems and email to someone from your iPhone.
Oh, I also bought at the ATT store an external battery case called a Mophie, you charge it, slip the iPhone in it and it supposedly triples your battery time. It uses it's battery first, then the phone's battery, it will charge your battery phone and you can keep it in your car for when you need it. $90 with tax, but worth it to me.
http://www.mophie.com