I have tried several ways to store them but nothing works as well as laying them between my mattresses. Its dark so they don't fade, its flat and the weight of the mattress presses them out looking nice and crisp for next year. I also keep all my poster board there as well.
The rest of the gnomes, fairy's and such get put in plastic bags (I use old bread bags and such) then into a bin in the bottom of the coat closet. This keeps everything near by and handy and out of a damp basement.