SDCardHolder.com, appropriately enough, sells this credit card-sized SD card holder.
I do a lot of video capture with a device that uses SD cards and keeping track of which cards are empty vs which ones have footage that needs to be processed is annoying.
These are $6.95 apiece on Amazon and come in multiple colors, so I can color code my cards. The SD cards in the blue holder are empty, while the ones in the yellow one are full.
