A script that will detect multiple images within a single image, crop them, optionally straighten them, and save them out with incrementing filenames+numbers. It was developed to aid in separating photos scanned on a flatbed scanner as one "image".
There is a big discussion thread over at gimptalk on this: http://www.gimptalk.com/forum/viewtopic.php?f=9&t=36438
The script also provides a batch mode to process a while directory of scanned images pages.
Note that the straightening will only work if you have the deskew plugin installed: http://www.cubewano.org/gimp-deskew-plugin/
***Since this site is down, i have attached a windows precompiled binary of the deskew plugin for convenience.