If you're an Android fan intent on being on the cutting edge of Android development, there's more chance than not you've heard of CyanogenMod. New releases of CM 10 allows users to upgrade to Android 4.2 on smartphones such as the Galaxy S3 model i9300.
The CM10 ROM for the Galaxy S3 is a nightly build, meaning the developers aren't confident enough to label it stable. The CM 10 nightlies have been reported to work fine, but bear in mind that their main purpose is to have users report bugs to the developers.
According to WCCFTech, CM 10 Android 4.2 nightlies are also available for the Galaxy Nexus (Sprint, Verizon, International GSM Version), Google Nexus 4, Asus Nexus 7 ( Wi-fi & HSPA+ Versions), Google Nexus 10, Asus Transformer TF700 Model, Samsung Galaxy Tab, Samsung Galaxy S, Galaxy S2, and Galaxy Note.
Visit CyanogenMod to download the CM 10 nightlies and for a full list of devices with Android 4.2 ROMS available.
If you haven't flashed a ROM before, be warned that things could go wrong and your device may become unusable. Make sure to read instructions carefully, and you can help play a role in the ROM's development by reporting any issues you encounter. If you're iffy, it's highly advisable to simply wait for a more stable ROM or official release.
Let us know what you think of CM 10 if you have the chance to download and test it out.