Is there any good photo organizer / viewer for the iPod Touch which allows you to use subcategories? I really need to have subcategories for my photos, or they'll be in a huge mess. Datacase allowed me to do this, but I just don't like the way it previews the photos. It doesn't preview them in full screen, but only as a small part of the screen, and it's very anoying to be forced to zoom in on every photo. So, back to my question, is there any good photo organizer out there?