The agile approach is one a lot of people are becoming familiar with. For one of our larger clients, we were doing 1 week sprints, and well, Im not entirely sure how it got started, but when a story was complete, someone would ring the gong sound, when a story wasn't complete, we could get the sad trombone... :(
Anyways, I threw together this little app which when opened, allows you to shake your laptop to make the noise.
You can toggle the happy or sad sound by hitting Option + Command + T.
Note: this is OS X 10.6 Only. Enjoy!