Most people will suggest a Channel Master 9521, which is probably heavy-duty enough for the job, but if you want one that will really last, and is far better built, albeit for quite a bit more money, the Hy-Gain AR-40 is the better choice.
http://www.hy-gain.com/Product.php?productid=AR-40
http://www.channelmaster.com/TV_Ante...p/cm-9521a.htm
Either rotator will work, but remember that you also need rotator control cable: the 9521 takes a 3 wire cable, the AR-40 uses a 5 wire system