StartNinja turns off the OSX Lion system start up chime / sound. It is a free utility that you can download here.
There are often times when I am in a public location and forgot to turn off the sound on my MacBook. Subsequently, a loud bong happens. Now there is a quick and easy solution for OSX Lion machines; StartNinja. StartNinja turns off the OSX Lion system start up chime/sound.
[crarko adds: Does what it says. There are some instructions on the download page. It's a useful utility if you need it.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120127215639478