iOS/Android: Popular app Bump has been around for awhile, allowing you to "bump" two phones together to transfer contacts, calendar events, photos and even Facebook or Twitter friendships. If your an iOS user, the newest version also includes music listening via bumps.
While we haven't actually mentioned the app before, we have mentioned its method of data transfer in PayPal's iPhone app. Bump, the parent application to API that made this possible, is available on both iOS and Android devices, and with just a bit of setup, allows you to transfer contacts, photos and calendar events to other friends with the app through literally "bumping" your phones together. It also allows you to become friends on Facebook, Twitter and LinkedIn through bumps.
The newest version for iOS also includes sharing music from your iTunes library. You can't save files to your friend's device, but you can bump them multiple songs and they can listen, find more music by that artist, and even view related YouTube videos. While we'd love to see full music sharing in the app, it's still nice if you're showing songs to a friend but don't want to hand over your device or headphones.
Bump is a free download for iOS and Android devices. At present, only the iOS version supports music sharing.