Mac/iOS: Most of us don't have all of our music stored on our iPhone and iPads, so it's hard to get music from one place to another. WiFi2HiFi makes it simple to stream music from your computer to your phone as long as you're connected to the same network.
WiFi2HiFi turns your iOS device into a wireless speaker for your computer. Install the free software on your Mac, and then open up WiFi2HiFi on your iPhone or iPad. As long as you're on the same network, you can then start streaming sound from your computer to your iOS device. Better yet, it works from any app, including iTunes, Spotify and YouTube. You also get a set of controls for pausing and changing tracks.
It works well and is surprisingly easy to set up and use.
WiFi2HiFi 2.0 ($0.99) [iTunes App Store]