John Lennon - Happy Xmas (War Is Over)

Happy Xmas (War Is Over) is a song that was "written" (see Skewball) by John Lennon with partial help from Yoko Ono (best known as the widow of John Lennon). It was recorded at Record Plant Studios in New York City in late October of 1971, with the help of producer Phil Spector. It features soaring, heavily echoed vocals, and a sing-along chorus. The children singing in the background were from the Harlem Community Choir and are credited on the song's single.
Closely related to the song: in late 1969, John Lennon and his wife Yoko Ono rented billboards and posters in eleven cities around the world that read: "WAR IS OVER! (If You Want It) Happy Christmas from John and Yoko." Five of the eleven cities included in the billboard campaign were New York, Tokyo, Rome, Amsterdam, and London.
In addition, it's been covered by Sarah McLachlan on her 2006 Christmas album, Wintersong.

Mariah Carey - All I Want for Christmas Is You

"All I Want for Christmas Is You" is a song written and produced by American singer Mariah Carey and Walter Afanasieff, and recorded for Carey's fifth album Merry Christmas (1994). Its protagonist declares that she doesn't care about Christmas presents or lights; all she wants for Christmas is to be with her lover. It was released as the album's first single in December 1994 (see 1994 in music), and reached the top ten in several non-U.S. countries.
According to The New Yorker, it is "one of the few worthy modern additions to the holiday canon".
In 2000 the song debuted on the Billboard Hot 100, peaking at number eighty-three for one week. This was because after 1999, singles were capable of charting on the Hot 100 without a commercial release and the song had received enough radio airplay to appear on the chart. Billboard magazine has since added restrictions to Christmas songs, but with the growth of all-holiday-music formats in the U.S., the song is played on the radio at the end of every year. Although the song is ineligible for the Hot 100, it peaked high on the Hot Digital Tracks chart during the 2003 and 2004 Christmas seasons. In 2005 it rapidly ascended to number one on Billboard's Hot 100 Singles Recurrents chart (for songs no longer eligible for the Hot 100), giving it a new peak. It also reached number one on the top 100 downloads chart at iTunes UK and iTunes USA, and became Carey's first number-one single on the Billboard Hot Digital Songs chart. In mid-November 2006 the song again entered the U.S. iTunes top 100.

You could also check this video featuring the Best Christmas Lights Display Ever