The default logoff sound in Windows 2000 is the most impressive three seconds of recorded music you could ask for. I had never heard it until this morning, in part because I don't wear my headphones all the time (I have no speakers at my workstation) and because I hard reboot my system more often than I logoff.
Similar in style to the default Windows Logon Sound, but simpler, the Windows Logoff Sound starts with strings (the same string sound as in the Windows Logon Sound), then continues with a piano playing four chords accompanying a female vocalist on pitch.
It tells the user, "Thank you for using Windows 2000, and have a pleasant evening. We hope that you have enjoyed your stay in our utopic, ethereal world. Please come again soon."
bigmouth_strikes informs me that this piece is likely the work of E2 hero Brian Eno.