It was just a few weeks ago that Google released the Android 4.1 source code to the Android Open Source Project which saw developers building several custom ROMs for Android devices.
You can download the official factory images for the Nexus S, Galaxy Nexus and Nexus 7 using the following links:
Following our the official factory stock images for the Google Nexus S. Please make sure you are downloading the correct image which corresponds with your device model.
Google Nexus S (i9020t and i9023) International variant [soju]
- Android 2.3.6 (GRK39f)
- Android 4.0.4 (IMM76D)
- Android 4.1.1 (JRO03E)
Google Nexus S (i9020a) 850MHz variant [sojua]
- Android 2.3.6 (GRK39f)
- Android 4.0.4 (IMM76D)
- Android 4.1.1 (JRO03E)
Google Nexus S (m200) Korea variant [sojuk]
- Android 2.3.6 (GRK39f)
- Android 4.1.1 (JRO03E)
Google Nexus S 4G (d720) [sojus]
- Android 2.3.6 (GRK39f)
- Android 4.1.1 (JRO03E)
Following our the official factory stock images for the Google Galaxy Nexus. Please make sure you are downloading the correct image which corresponds with your device model.
Google Galaxy Nexus (GSM/HSPA+) [yakju | maguro]
Google Galaxy Nexus (GSM/HSPA+) with Google Wallet [takju | maguro]
Google Galaxy Nexus (VZW CDMA/LTE) with Google Wallet [mysid | toro]
Following our the official factory stock images for the Google Nexus 7. Please make sure you are downloading the correct image which corresponds with your device model.
Google Nexus 7 [nakasi]
Google Nexus 7 [nakasi]
One notable absentee is the Motorola Xoom (Wi-Fi) which is also a Google Experience device. We will hopefully see the stock images for newer versions of Android appear soon after Jelly Bean has completed rolling out to Xoom owners.
source – Google