The doubleTwist developers have introduced the ability to stream Google Play Music to AirPlay devices using MagicPlay, their own personal means of streaming music from Android to an AppleTV or AirPlay-compatible speakers. The process taps into the same API that Google uses to stream to the Chromecast and that which Sonos uses for Google Play Music to stream to its devices.
A new app just hit the Android Market that helps bridge the gap between Google TV and iDevices that use Apple's Airplay technology. The app is called Airtight, and it allows you to stream non-DRM movies and images directly to your GTV. In its current state the app cannot stream DRM content or music, but the developers note that they are working on support for the latter.
The app will only set you back $0.99, so if you have both an iDevice and Google TV, it's definitely worth grabbing.