During my last trip to NYC I met one of the guys behind Mobile Roadie in Williamsburg, and was quite impressed with the app. Basically it allows any band to generate an iPhone app for their band, get it up on the app store, and continually update the app's content with minimal effort.
You probably already use your iPhone to get directions, play music, or look up movie times, but did you know you could use it to see whether your favorite restaurant has received a food safety violation?