This is what you (and I) want. Unfortunately they want $286 for the meter, $170 for a power supply ($10 at Radio Shack) and $85 shipping! Bleah! And oh, did I forget to mention you also have to buy a $235 "Reset fob" to reset the pint counter back to zero? Double bleah!
http://www.flowmeters.co.uk/turbine_meters.htm
Why can't anyone make one similar to this with a reset button: ?!?!?!
http://www.omega.com/pptst/FTB4000.html
Don't know if the beer would be foamy after going thru the turbine.
Also, Google for "KegBot" for a fun idea.