Party DJ

Party DJ is a music queueing app you use with your friends.
Party DJ will shuffle all of your music, or your choice of playlist(s), and allow you and your guests with smartphones to vote on what tracks will play next. Tracks with more votes move up and get played sooner.
Guests can queue up songs from your library and those from their own (if they have an iOS device)
Party DJ has a free companion remote app called Party DJ Remote (also available in the App Store) and a web interface for guests without iPhones.

"Party DJ is impressive in how it “just works” and brings back an old feature while adding new options thanks to iOS 7 and Bluetooth. I had a lot of fun testing Party DJ at home and I can see it being used at family gatherings or parties where music democracy can be the best solution to settle arguments over what’s playing." - Federico Viticci, MacStories

Please Note: Party DJ currently works only with music downloaded onto your device, so if you use iTunes Match you will need to download tracks to your device to play them in Party DJ.