If you have sheet rock walls, medium length common pins will work fine for smaller panels, say up to 2' x 2'. Be sure the head of the pin is secure (many plastic tips will come off rather easily), and that you try to distribute the weight evenly using multiple pins. For bigger panels and/or items like rigid diffusion panels, I use quiltmaking "T" pins. All leave minimal marks, are easily repositioned, and hold a surprising amount of weight.
-Richard
-Richard