Sound Shuffler for Mac

From No-U-Turn Software:

Sound Shuffler is a control panel that randomizes the Mac system alert beep. It also plays sounds in a 'Sounds' folder located in the System Folder. Just drop sounds in this folder and Sound Shuffler immediately takes advantage of them. Sound Shuffler plays all sounds asynchronously, which means they will play without hogging the processor. This allows you to continue to work while your sound is playing. Any sound can be stopped by pressing the 'Esc' key. Sound Shuffler even lets you play sounds at random times, using the random sound slider in the control panel. You can set the length of the delay that Sounds Shuffler awaits.