I've had pretty good success with Sprint Enterprises' Beer Guardian.
It's based on a in-line turbine design that measures beer usage for each beer line without weighing, etc. The best part is also its simplicity.
A simple digital counter is mounted in our office (the measuring turbines are at the kegs in the cooler) and we take beginning and ending shift reads of each meter. A simple calculation of sales into ounces vs. usage in ounces and voila instant control. A simple form can suffice for perpetual inventory tracking and later calculation.
Of course, depending on the number of stations, etc., you may want to add more meters for finer accountability. But it won't impact the beer quality or taste.
As for beer line cleaning, we simply take a reading before (before the existing beer inline is pushed out) and after the cleaning (after the water rinse but before the new beer is pushed through) to eliminate the cleaning from our measurement.
You can get more info at
www.sprintent.com