I thought I would share this with everyone as I know that often people have a hard time finding materials to build prototypes with. Most companies that sell bookbinding materials won't sell to the public and if they do they tend to sell you stuff in volume. These guys aren't always the cheapest BUT they will sell you materials in cut yardage and will give you access to other tools that the trade uses.
I thought I would mention this as I have seen a lot of people posting how to's on things and one thing that I think I lot of people might not have access to are good materials to cover the backs of boards or other pieces with. I saw someone recommend using duct tape as a way of protecting your board. Talas has a number of different materials you could use for this kind of thing. The best section to search for suitable materials for this kind of application would be in their Fabric and Textile section under Book Cloth Starched. The Cialux and Iris in the paper backed section could also work but I would suggest the materials in the Starched section. You will also find in the Supplies section proper board and tools.