If you're feeling extra fancy, you can make them all black and white before printing them out. Get the super-simple how-to here. It uses mini clothespins, but normal-size clothespins would totally work, too.
large Foam core boards to brainstorm ideas. Ikea Benjamin stools hacked to keep the boards upright. They can still be used as stools when needed and are also great for creating temporary walls for project spaces.