Mute the Mac Boot Chime with StartNinja for OS X Lion
Macs have always had the classic boot chime that announces the system has begun startup or has rebooted, but if you’re in a quiet place you don’t always want that sound to play. You may know that you can temporarily mute the Mac by holding down the Mute key during boot or reboot, but if you are looking for a more permanent solution, check out StartNinja. A free and simple utility that gives users the ability to disable the startup chime, StartNinja will keep the Macs boot sound quiet while allowing the Mac to retain normal sound function otherwise.
For those running Mac OS X 10.6.8 or prior, holding mute works on a per boot basis, or there is a system preference panel that gives the same ability to disable the boot sound.
Thanks to vijay for the tip in our comments