Since this will be the Official Ringtone thread, I thought I would repost this site..
http://www.research.att.com/~ttsweb/tts/demo.php
This is a speech-to-text site that is very easy and fun to use. It saves the audio files in a wav. format which is convenient for notification sounds.
Just drop the .wav file into the windows folder.
EDIT: Didn't notice this link was already posted in this thread...1000 apologies.