If your music is in your itunes, then its already built in to iOS, use homesharing to access your music in your itunes library over your wireless network.
I followed instruction everythuing is ok (itunes is sharing etc.. etc...) the problem is on my Ipad I don't see any "library" wher i should find the home sharing !!!
Try the 'Remote' app on the app store (Grey icon with blue play symbol) you can connect to iTunes and control the music off of it.
TunesRemote also allows you to control music on other apple devices.