Tire Shootout!
How about a series of tire tests? Tires are probably the most important bike part for safety, comfort and performance and the most frequently replaced. An annual tire shootout of one general purpose bike using several major brands over a variety of useage conditions would be valuable.
An alternative would be a series of short articles by your testers every time you change the rubber on one of the bikes in your mighty test fleet. What you test would depend on the purpose of the bike. Another excuse to go riding, guys!