Here's a pretty gnarly portable photo storage device from the Japanese company "ELEVE." It is the "ELEVE Photo Binder 20GB," and among other things, measures 69 x 79 x 22mm (H x W x D) or 2.7" x 3.1" x 0.9." In other words, it isn't much bigger than a MiniDisc as far as height and width are concerned. It has not a card slot, but instead provides USB On-The-Go functionality; by connecting directly to your digital camera (or whatever) via USB, its contents can be downloaded directly to the Photo Binder for posterity. Transferring these files off the ELEVE to your PC when you arrive back at home is as simple as connecting it to your PC. And for some reason, it has an organic EL display instead of just a plain old LCD one.
"ELEVE Photo Binder 20GB" from Toyota Trading Corporation [DC Watch]