"The Nutcracker" is one of the most beloved ballets of all time. This is partly because of its Christmas setting, so it's guaranteed an audience every year, but mostly because of the amazing music of Pyotr Ilyich Tchaikovsky. The fact that there are several roles for children doesn't hurt either as it makes it very family friendly!
"The Nutcracker" is such a part of the Christmas season I can't imagine December without seeing it at least once. If you can't see it live, this is a brilliant and timeless performance, my favorite.