i have a few, but apps have to support airplay, try searching for anything starting with Air*******. I use a Mac, and i have Airserver installed, which can be installed on iOS devices too.
i have other apps, just cant remember their names(maybe 5), but airserver is all i need.
I found something called airmusic, but after an mail to those guys, they said that streaming an app in the background wasn´t possible, just the ipod song..
An cable is not working for me, so the hunt goes on...