Paintbrush Rack - Magnetic knife holders sold at kitchen-supply stores can be mounted to the wall with a few screws and will keep paintbrush bristles from being squashed. Hang the brushes bristle end down for proper drying and to minimize the amount of dust that collects between the bristles. You can also store other metal tools and utensils this way.
Also on these boards
Paint Brush Coat Hooks - ha ha finally a use for all those brushes we ruin!
Making your own paintbrushes