This script changes a rainy landscape to a sunny one.

Copy it into the scripts folder from GIMP, you will find it then under Filters -> Light and Shadow -> Sunny Landscape.

If you like it, hug someone.

Before:
http://www.flickr.com/photos/srgblog/2477297713/


After:
http://www.flickr.com/photos/28653536@N07/4477835346/

Update1: Added a desaturation layer and changed the hues to less obtrusive defaults.