This app has been available since the early days of the App Store, however the whole time, it has seemed to be the best of the streaming audio applications available, however the interface is slightly less than intuitive.FStream has a built-in library of presets including ShoutCast and the iTunes presets, however there is functionality to add in a custom feed. I’ve really only ever used this app to receive the TWiT.am audio feed (twit.am/listen). I am aware that there is a specialized TWiT.am app in the App Store, however it doesn’t seem to be as resilient to a slower connection (*cough* EDGE *cough*) as FStream.
You can get FStream in the App Store for free. It is compatible with the iPod Touch and iPhone (3.0 not required.)