Since Android Police leaked the updated Gmail application a few weeks ago, a number of other applications from Android 4.2 have been leaked online. You can now download the entire system dump from the LG Nexus 4, but it probably won’t do you much good. Some helpful people around the internet have packaged some of the applications into zip files that you can install on your Android 4.x devices right now. The keyboard, camera and gallery all seem to work fine on my Nexus S, but the clock force closes when you try to add an alarm. Apparently, Galaxy Nexuses do not have this problem. Click the links below to download the various components, and then flash through your custom recovery:
Hopefully Google will push the new, updated Jellybean to AOSP and Nexus devices within the next couple of weeks, but hopefully these leaks will be enough to tide us over until then.