Most of my patterned paper is either bought by collection or the new paper pads that most companies are selling now instead of collection kits. They are stored in Cropper Hopper Paper Envelopes along with their matching embellishments. These paper envelopes have been discontinued but you can get something similar at Michaels in their storage section.
When I use up a collection or when I buy single pages of patterned paper, I store it in this Advantus Rolling Cart with 12×12 hanging files. I sort most of them by manufacturer but the plainer patterns (like polka dots, etc) are stored by color.