I have completed an ultrasonic anemometer for my weather station.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1268871131
Download UltrasonicAnemometer.zip from
http://sourceforge.net/projects/arduinoweather/files/
This project is a prototype of a non-trival design. As such I expect there will be significant improvements which can be made to both the circuit and the code.
If you do find improvements please share them with the community on this forum.