Thanks again to the venerable JBQ of Google, the unmodified factory image of Android 4.0.4 for the Nexus S 4G (sojus, Android 4.0.4 IMM76D) is now available here. As JBQ states on Google+, this image is for those among you who have flashed to custom versions of AOSP and want to get back to factory state. No, by the way, there's still no word on an OTA update yet.
As with all the others, the factory images are available on the Factory Images for Nexus Devices page.
To get started, head to JBQ's Google+ post on the subject, where he has more info on a known bug where the device reports an incorrect radio version number. Be sure to read the post, as well as all the comments, for more information. As usual, if you're not sure what something does, don't flash it.