“White Christmas” is an Irving Berlin song reminiscing about an old-fashioned Christmas setting. According to the Guinness Book of World Records, the version sung by Bing Crosby is the best-selling single of all time, with estimated sales in excess of 50 million copies worldwide.
Source: http://en.wikipedia.org/wiki/White_Christmas_(song)
YouTube Link: http://youtu.be/9Yg5g_Xl-uU