Not sure if this belongs in Post Processing or General Photography.
If it's there, I need to try it: My recently acquired Nikon D5000 has an in-camera retouch menu. One of the options is image merging. It combines 2 selected photos and merges it into one new RAW file.
Here is the one that gave me the best result. It sure does not work on all pictures, but some results are really surprising!