1. SLIDE SHOW
Now that we can go NEXT and PREVIOUS through the images in the lightbox, add a slide show capability. This would automatically take the user through each image. Perhaps some checking of the media type might be needed. (I wouldn't expect a slide show to automatically move past a .wav or .avi file.) Perhaps the slide show would be initiated by pressing a button from the top level. Let the user set the viewing duration and whether or not to continually cycle through the images once reaching the end. The implementation might done using a simple meta-refresh or javascript.
2. SHARE WITH OTHERS
Allow the lightbox to be shared in a read-only mode with others. Much like sending a postcard, this would let a user collect images to their lightbox and then email a URL to someone so that person could view the contents of the lightbox.
3. SEND SLIDE SHOW LIKE POSTCARD
Expanding on the above, also allow a user to send a URL to someone to view a slide show of the lightbox.