Every year here in Philadelphia, WBEB-FM begins playing Christmas music 24/7 starting in August. Well, it feels that way to me anyway (though my wife wishes they really did start that early.)
At any rate, B101 also polls visitors to their website as to what Christmas songs they want to hear most each year. This quiz is based on the 2007 poll results, the most recent I could find. There are numerous duplicates, so a handful of good guesses will get you close to 50%.