Ohhh, organizing, my fav! I LOVE organizing (seriosly, love-love-love it!) and while a good portion of my vintage stuff is unorganized that isn't listed, I do have a system in place for everything that has pictures and is ready to post.
For my digital stuff, I number the end of my title with a specific code that will let me identify it quickly (ie: Mother's Day is M1--, other codes are 2--, 10--, etc). This way, when I sell something, I go to my shop fold on my hard dfrive, pull up the corrent basic file (M1--, 2--, whatever) and then locate the file folder labeld with the corrent number (228, M104, etc), open it & there's my postcard!
For my vintage, I've used a standard method that I've used for years and tweaked it for online. I sort everything based on matterial (glass, linen, 'shabby chic', 'kitchen') and then label my boxes with large computer labels based on the grouping in the particular box (green glass, blue glass, tablecloths, runners, etc). For online, I will label the box with a number under the current description (148A, 148B, 214A, etc). This way, I can identify that blue glass is in all boxes marked 148, and I just need to match the number in my listing witrh the box in that series (A, B, C, etc). I used small boxes that I get from the Little Debbie vender (big enough for several pieces of glass, but no more than a dozen, maybe). If you ask a vender for boxes on a Monday when they are restocking the shelves you can generally get at least a dozen boxes that are all the same size or nearly the same size, which makes stacking and storing so much easier!
As for all my paper stuff from either shop, I keep them in plastic totes under my bed. One side of my bed has clothes, the other side is all totes with paper. Plus, I cleared out a drawer in my dresser for a good amount of buttons, also. :-) The vintage stuff is stored downstairs in the black hole vortex. THAT is something I've been trying to fix, but if I'm down there too long it (the basement) sucks the will to organize right out me and I'm tempted to just throw is ALL away :-P