Here are a few that you might like:

http://www.oringz.com/ringtone/tiny-bell/
http://www.oringz.com/ringtone/oringz-w445/
http://www.oringz.com/ringtone/oringz-w444/
http://www.oringz.com/ringtone/oringz-w433/
http://www.oringz.com/ringtone/oringz-w432/

I picked out the short and not so loud ones, but there are many more listed under the Notifications category. All have previews so you don't need to download to play.