But Sadun found that you can change the Notification Center sound with a bit of a hack. If you go to ~/Library/Sounds and place a sound in AIFF format there, and name it Basso.aiff, Notification Center will use that sound. You'll need to run the following Terminal command to relaunch Notification Center (or restart your Mac):
killall NotificationCenter
You'll have a much better sound for notifications. I really think Notification Center should not only allow users to change the default sound, but also choose specific sounds for different applications, the same way you can choose a specific ringtone for different callers on iOS.