Home Alone (1990)
This film can never fail to cheer me up, and I've seen it many times. It's a bit hard to watch at first, I want to punch Buzz, and I want to punch Uncle Frank even more.
Watching as an adult, I find Kevin's parents downright harsh for sending him to the attic for an incident that seems really minor, but that's just my two cents worth.
I always look forward to the Tom and Jerry style sequence where he evades the bad guys - also, the story involving the neighbour is heartwarming.
Definitely one to watch at Christmas, as is Home Alone 2, just don't bother with any of the subsequent sequels.