I often have to rotate my photos to the proper orientation, because my camera doesn't have position sensor. I'd like to do this operation without loss of quality, so I discovered exiftool, which simply rewrites some exif tags. The exiftool itself is a command line application, so I've created a simple GUI in AppleScript. The script is follows:
Save the script as an application and simply drag the image (it should also work for multiple images) on the app. You will be asked which side to rotate. It may happen that you will have to adjust to values in the script (8 and 6); these values work with my camera. I personally use the app as an external editor for iPhoto.Mac OS X Hints
http://hints.macworld.com/article.php?story=20091009130431630