I used to use the Cropper Hopper storage files already linked, but I did not care for them at all. I now have paper display cabinets that I bought from a LSS when it was going out of business.... I absolutely love them! If you have a chance to buy them (and have the room for them) I'd recommend it.
My friend has her paper in Sterilite boxes without the lids; I wish I could remember what size they are, but 12x12 paper fits perfectly in them. I'd guess that they're about 13" wide by 13" tall and maybe 10" deep. She made dividers and stores all of her paper vertically. It's really easy for her to flip through and if she comes over to my house to scrap, they're also easy to bring with her.