OnSong for iOS is an iPhone and iPad application that turns your phone into a neat little chord sheet tool. From the app's description:
With OnSong, you can manage huge collections of chord sheets for your band or worship team on a simple, lightweight device. Quickly pull and reorder lists and flip from one song to the next with ease. Transpose and highlight chords or change font size with a brush of your finger! Playing music has never been more simple. This software is built for live performance musicians.
The cool thing to me is that once you get your score sheets into the system you can share them with your fellow musicians via a Bluetooth connection between phones/iPads
The app is normally $4.99 but if you act quickly they are giving it away for free for a limited time.