Google has released the official Android 4.0.4 factory images for the international (GSM) version of the Samsung Galaxy Nexus and the T-Mobile and European unlocked Nexus S. These are files that allow you to return your Nexus to stock, no matter how badly your system software gets screwed up. With these files, you'll always be able to return to stock Android 4.0.4 (build IMM76D). Everything is included and when finished flashing these, it will be as if your phone had been left pristine and ran all the OTA updates.
The files could also be of use to Nexus owners who want to update to 4.0.4 with a clean start and nothing left over from before. Remember that flashing these system images will wipe all data from your phone, including music, pictures or other media. If you just want to update your GSM Galaxy Nexus from 4.0.2 to 4.0.4, we've got that covered too.
To flash these system images, you'll need to be comfortable with fastboot and the command line, and you'll find a "flash-all" script packaged with the images to help you get started. Check the source below for Google's downloads links.