Google just released factory image files for Nexus devices. These images will wipe data on your device and restore to original factory state

Factory Image "soju" for Nexus S (worldwide version) 

Factory Images "yakju" for Galaxy Nexus "maguro" (GSM/HSPA+)

Source http://code.google.com/android/nexus/images.html 

Links are for GSM versions

Nexus S Android 4.0.4 link http://android.clients.google.com/packages/ota/google_crespo/hR7QFEtn.zip

Samsung Galaxy Nexus  http://android.clients.google.com/packages/ota/google_maguro/7f97fbc19417.signed-yakju-IMM76D-from-ICL53F.7f97fbc1.zip

If your update fails with "Status 7 Erorr" like mine try this:

Download Android 4.0.3 (Android 4.0.3/IML74K/XXKI1 Radio/KL1 Bootloader) full rom from http://android.clients.google.com/packages/ota/google_crespo/ZD3PyN0t.zip

Copy it yo your sd card

Reboot and select recovery mode with VOLUME UP + POWER, when you see android icon with exclamation icon press POWER + VOLUME UP and apply it from sd card.

Then, reboot to boot loader and flash clock work recovery (http://download.clockworkmod.com/recoveries/recovery-clockwork-5.5.0.4-toro.img) with "fastboot flash recovery recovery-clockwork-5.5.0.4-toro.img" command from your computer.

Once, this done; select recovery without rebooting your phone and apply Android 4.0.4 from your sd card