When attending meetings, I commonly kill the sound to my powerbook by putting a plug in the headphone jack, rather than turning the sound down to 0 (its quicker and no one will hear me if I have to reboot). This creates a problem in that I can't tell if a beep occurs (menubar flashes only when sound level is 0). Therefore FlashBeep.
Because I'm lazy, I use PatchWorks to patch _SysBeep, so I only actually had to write about 4 lines of code (i.e the icon took me about 20 times longer to draw). It checks the current sound level for 0, so it only flashes once in any case.
Things I wanted to do but didn't quite have the time (and I turned it in at the last minute as it was):
A control panel to control its behavior
Adding a behavior to flash the whole screen rather than just the menu bar
