We had a similar question come up last night during the Q&A session of the general meeting.
You should also look into Graphic Converter. It has a batch convert feature that is very powerful. You can do things like rename files, change their color depth, crop them to a specific size/aspect ratio, resize them by a percentage, and much more, all at the same time.
There are also some shareware utilities (I haven't tried these out, just heard about them)...
EasyBatchPhotoPhotoDropEasyCropImageWell