A few years ago, I've created an iPhone app called "MySongbook - Lyrics & Chords", that helps you manage your collection of chords sheets for your favorite music. You can see it here on the App Store:
It's been awhile since I last update my app, and I'm currently in the process of updating it to support iOS 7, and require a new app icon that would fit the new OS as well as communicate a refreshing new start for the app.
It's important that the icon would stand out amongst the many other apps in the same market. It's enough to look at selected apps by searching for "chords", "tabs", or "guitar" on the iTunes app store. I also prefer that the dominating colors would be based on the warm colors of acoustic guitar, but feel free to deviate from this requirements if you choose so. Examples of the guitars I had in mind:
Also, despite the name of the app, the icon doesn't need to resemble the appearance of a book.