GuiMags are clever rapid UI wireframe prototype tools, instead of drawing common elements like buttons, you just stick one of these common UI elements like fields, tabs, buttons etc. Then use the dry eraseable magnetic surface to give it a label.
Makes the UI much more consistent than handdrawing AND they can be easily moved around.
They are great if you like whiteboard sessions for IxDA, especially in a team.
More Info http://guimags.com/index.php?p=products_guimags_corporate&nav=nav_guimags