I recently used the retrosheet play by play database to count how many times runners took extra bases on hits or advanced on fly balls to the outfield. The flip side of this would be to count the number of times outfielders either threw runners out trying to advance or prevented them from advancing. This would be one way to measure the effectiveness of an outfielder's arm. John Walsh at The Hardball Times has done just that. Thanks to Kurt for directing me to this article.
Magglio Ordonez was the third ranked right fielder in the Majors saving an estimated 7.2 runs per 200 opportunities. He was behind only Alexis Rios and Brad Hawpe. Curtis Granderson was below average for center fielders giving up up an estimated 4.2 runs. Craig Monroe was the 4th ranked left fielder saving an estimated 4.2 runs.
So Granderson had the best range of the three out fielders but Ordonez and Monroe had better arms. Now, I believe range is significantly more important than having a good arm but Ordonez and Monroe are somewhat underrated if you evaluate on range stats alone.