SleepMute

SleepMute automatically mutes & unmutes sound. Don't let your computer disrupt a quiet shared space with unwanted alert sounds at all hours of the night, let SleepMute keep the peace!
Features:
✹ Mute and unmute when the screen saver starts, display sleeps, computer sleeps, or computer restart, shutdown, & logoff.
✹ Fade sound in or out over 1 - 5 seconds.
✹ Mute or unmute immediately instead of fading.
✹ Privacy.

Stop prying eyes and ears from knowing what you're watching using a Mac OS X hot corner to sleep the display and mute sound.
COMPATIBILITY NOTE: Currently only supports muting startup sound on built-in speakers, not externals.