Android 4.2 comes with a few cool new features, one of which is a new Camera and Gallery app with a new interface and the ability to create "photospheres". Here's how to get it on a rooted, non-4.2 phone.
The process is pretty simple: all you need to do is head over to this thread at the Android Central forums, download the necessary files, and move them to the correct locations with Root Explorer. If you own something other than a Galaxy Nexus, you may need to edit your build.prop file, but that's pretty easy too.
When you're done, you should have a fully functional Android 4.2 camera on your device -- though the photosphere will only work if your phone has a gyroscope inside. The camera may also be a little buggy on certain phones, so proceed at your own risk. Check out the full instructions over at OMG!Droid for more info. And, if you want more 4.2 goodness, be sure to grab the new swipe-enabled 4.2 keyboard for your device, too.