OnSong for iPhone
Hit The Road
OnSong is a universal app you can use on your iPad, iPhone and iPod touch. While not the best for performing live due to the small screen size, you can use it to pick your sets, practice your gig and import and organize your music on-the-go.
The best news is that if you choose to upgrade to an iPad later, you can install OnSong for free and transfer your OnSong library.