ExifTool is the best tool to deal with EXIF data!
You have to try it to see that. Any type of EXIFs, read/write according the RFC (and sometime more :)) )
Rather fast, though perl. It has anything you could wish.
I use this as a command line tool to check exif and do time corrections too, it's a great tool and supports more than images, hell, it will work with pdf metadata, video, mp3, etc...
It also a very easy to use perl library, so it's very nice to program scripts that would need to access the file metadata.