THX's new app costs $2 starting next week, and is made to turn your iPhone/iPad/iPod touch into a home theater calibration device.
What's the upside to this over the THX calibrator on various DVDs and Blu-rays? You can use the phone/tablet's camera to do color and tint calibration instead of shelling out for blue filter glasses (which aren't cheap or easy to come by).
You can calibrate video via AirPlay and an AppleTV, but to do sound you'll need Apple's iPhone/iPad to HDMI adapter: Lightning connector version, 30-pin version.