I think you can probably figure out the app from the title. I’ll let L3v5y speak for himself though: It integrates with the Pictures hub, and the Music+videos
Here is another cool windows phone 7 app called Roboprint. This app allows users to print to any printer any where as long as you install a small app on the computer
I think we can safely say that Windows Phone 7’s success will rely heavily on the applications that will be developed for it. Apps are the corner stone