Oh! Oh! I have a great suggestion! When it is pissing down rain, go see The Sunshine State - if it's still playing! It's a movie by John Sayles* (Lone Star, The Secret of Roan Inish, other great movies) so it will probably be playing in your more arty theatres, but if you've got the grey blues (er, you know what I mean), seek it out!
I recently saw it with a friend of mine, on a rainy dark afternoon. It's set in Florida, just about life there, looking at the lives of two women going through similar things, that is, asserting their own lives from the lives their parents wanted for them. And these are women, not girls in their 20s. Angela Basset is one of them, I wasn't familiar with the actress who played the other, but she was good - all the actors were. You get blasted with about two hours of pure Florida sunshine, and a nice, funny, slow (makes the sunshine sink in) story to go with it. I was so involved with the movie, when we left the cinema I was shocked to be back in Belfast in the rain. It kinda sucked (to be back in the rain) but the movie is a real pick-me-up if you need a fix of sun.
If you can't find that movie, then rent a sunshine filled movie to watch. Although to get the full effect it's probably better to see a sunny movie in the theatre.
* John Sayles is very good at capturing the feel of whatever place his movies are set in, and he succeeded with capturing the pace and feel of the small town in Florida in this movie. He also has a way of exploring the different cultures and race relations in the States that is worth watching and thinking about. I can't say enough about his movies. Everyone of his I've seen has been wonderful.