I heard about this on Download Squad. I haven’t tried it myself, but it sounds interesting.
While it can’t bring back the quality to a heavily compressed JPEG image, JPEG Enhancer can smooth out the artifacts and make a much nicer-looking image as a result. It’s so easy to use, it’s ridiculous; simply open a JPEG image that you would like to fix, set the filter slider at the bottom, and press the Process button to see the results. Once you have it set to your satisfaction, save your new image and you’re done.
JPEG Enhancer recently became a free download, so what’s to lose?
You can learn more about the software and download it by visiting the VicMan Software web site.