photools.com IMatch Overview - Import and Export
Wow. They are SERIOUS about letting data flow in and out. A big plus. I also looked at ThumbsPlus for image management on the PC. It uses an Access database, so it's very easy to get data in and out, but I found the scanning workflow awkward. I was using a beta so I couldn't consult the help files to learn more.
IMatch costs $50, so it's not extremely cheap. I do like their attitude though.
Maybe they'll do a Mac version :-).
Update: Still not quite right for my scanning project, the workflow is too awkward. SnagIt may still be my best bet, together with some renaming tool. (SnagIt bogs down with even small image collections because the browser regenerates the thumbnails on each viewing.)
One surprise with both ThumbsPlus and IMatch is one can't create an EXIF header for an imported JPEG. One can edit existing EXIF data, but one can't add new data. This is very annoying. I'd like a scanned image to have an EXIF data for when the image was taken, not the date it was scanned!