'It's a wonderful life' (1946)
Lovely film. The Duke of Yorks usually show it at Christmas, so perhaps a BAF outing to the cinema on the cards? I haven't seen Slapshot I must look out for it.
I feel like a kid in a candy shop, I think I'm going to have to do two lists here. One where films I think are therapeutic/funny and the other, at risk of being the Fraser Crane of the forum (unless anyone else is bidding for the role

), my personal favourites, which are a bit arty.
High AnxietyThis has to be at the top of my humour therapy list. Mel Brooks spoof of Hitchcock films. Just hilarious. Brooks is a newly appointed director of the Psychoneurotic Institute of the Very, Very Nervous.
http://www.imdb.com/title/tt0076141/AmelieThis is actually on both lists and probably the film I am most likely to watch to cheer myself up. If you don't mind subtitles, this is a most wonderful film about a character with social anxiety. It is very hard to make films about a sense of lonely isolation, without the film being depressing but this film manages to be beautiful, funny, wistful and still capture our atomized lives.
http://www.imdb.com/title/tt0211915/Eternal Sunshine of the Spotless MindThis is a film about memories and a love story in chronological reverse. Jim Carey plays an introvert and Kate Winslett an extrovert. I think it also brings out emotion for me as my mum suffers from dementia.
http://www.imdb.com/title/tt0338013/Jay and Silent Bob Strike BackYou may have to be a Kevin Smith fan for this but it is an outrageous slapstick, stoner road movie. It is worth watching just for the most sophisticated fart joke of all time.
http://www.imdb.com/title/tt0261392/Stardust MemoriesI felt I had to throw in a Woody Allen film and this is my favourite.
http://www.imdb.com/title/tt0081554/I find favourites change over time but these are pretty much my five top films:
La Dolce Vita, Donnie Darko, Amelie, Eternal Sunshine and Alphaville.