For the best boards, I use 19x9x3 or 22x10x4 top loading boxes from shippersupply on ebay, which are actually from Uline. They arrive boxed within another box and are very high quality. I just use a sharpie to write on the end of the box.
For the rest, I store them sorted by switch or intended use (keep/sell/harvest switches) on their edges inside large boxes. Like file folders in a filing cabinet. That way there is minimal pressure on the keys and the cords aren't getting smashed and tangled up.
haha i have the exact same method for sorting/storage, guess it's just common sense.
The bookcase noted in my previous post is basically my "trophy case", for long-term storage. Most of those keyboards are boxed and then sealed with cellophane (to minimize oxygen exposure).
Then there's my daily drivers, which i need easy access to. They're neatly boxed and labeled in my office closet.
For shipping, Uline is pretty cheap (something like 1.50 per) when you order 200+ boxes. I will eventually go that route, but my collection isn't that big yet. Thing is, there are so many people trying to get rid of cardboard boxes that I can't justify the price. Tape and packing material are cheap, and years of working shipping/receiving for small businesses has turned me into sort of a box wizard. It's hell on the hands, but that's why i keep one glove filled with vaseline.