One of the greatest parts of owning a Nexus is the software support from Google. Now this goes beyond just updates, as Google also posts complete "factory images" for Nexus devices so that willing hackers can always return their devices to stock firmware through first-party approved methods. Things got a little sticky when the Verizon Galaxy Nexus and Sprint Galaxy Nexus (and Nexus S) were released, however, because they included closed-source bits related to CDMA and LTE. This put a damper on Google's ability to release the images for anyone to download.
Thankfully, the Sprint Galaxy Nexus ("mysidspr") now has a complete image available for download by anyone that includes everything you need to return your device to stock 4.1.1 Jelly Bean. Additionally, Google has posted the 4.1.1 factory images for the Sprint Nexus S 4G ("sojus") and 4.1.2 images for the AT&T Nexus S ("sojua") as well. It's good to see Google not leave out older hardware, even though it's two Nexus revisions behind now.
The process is pretty simple if you've got a little bit of patience. Need help using these tools? Head to the forums, there's plenty of great info and helpful users at the ready.