Speedy Clipping Mask
Sometimes a masked layer is just an Option-click (PC: Alt-click) away. Simply click-and-drag the layer to be used as a mask directly above the layer to be masked. Press-and-hold Option (PC: Alt) and hover your cursor over the horizontal line separating the layers. The cursor (hand) becomes a Clipping Mask icon; just click on it to convert the layer above into a mask.