Some of these choices include making sure the tower is sized correctly to begin with, incorporating better fans, including variable-frequency drives (vfd's), adding new or more efficient fill, or using a new set of nozzles to give better distribution over the fill. But it's important to remember that a cooling tower works as a system: Adding an oddball combination of components might not solve a problem, and indeed, it could make existing problems worse.
That's very important today, given that energy prices are ratcheting upwards every day - it pays to look at every component in a system to make sure that each one is saving as much energy as possible. With cooling towers, the water should be as cool as possible when returning to the chiller.