Google have made the default Factory Images for the GSM Galaxy Nexus available for everyone to download. The Images allow you to flash your Galaxy Nexus back to factory settings after having any kind of crazy ROM installed on your device. Everything is included in the Images: bootloader, baseband and system image. It is noted that you also lock your bootloader after flashing back to the factory build using “fastboot oem lock”. More advanced details and the actual image in the source links.