When people say "stock Android experience", they usually think of the Google Nexus phones. Believe it, if you download the source code from Google and compile it yourself, you don't get any of the nice Google apps, such as Android Market, Maps, Gmail, and even Google Search. Even the boot animation isn't the same flashy ones found on the Nexus phones. In fact, it's just a boring green Android logo, which is the same found on the Android SDK Virtual Machine (pictured here).
I was curious about compiling the code myself, since Android is open source. If you're curious of what it looks like, make sure you root and backup your current phone, then flash the correct ROM image.
These are only for the GSM versions of Nexus S and Galaxy Nexus. Crespo is the codename for the GSM Nexus S, and Maguro is the codename for the GSM Galaxy Nexus.
Notes: I included Google Apps and Face Unlock as separate download. You will have to disable the built-in Search by going to Manage Apps to enable Google Search.
Warning: Root is not included. Please obtain root from Wug. This will also restore your recovery back to stock. Again, this is a straight AOSP ROM compiled from Google's source.