I know it's a bit too easy to go with Vince Guaraldi, but this song is always the first I hear when the season comes around.
There's something about the delicate touch on top of the waltz-like rhythm that perfectly depicts the dichotomy of delicateness against the sheer brilliance of a snow covered landscape. You would think it's for that scene in the opening where the Peanuts gang and Snooby are enjoying a day of shenanigans on the frozen pond, but it's actually played over a scene where Linus and Charlie are walking along a snowy street, in a philosophical discussion as the occasional snowflake flutters down. It highlights the metaphor of Linus' introspection against the general innocence of the two boys.