Don't know the keyboard shortcut, but if you have your foreground color set to black and hold down the opt key clicking on the mask [0] icon at the bottom of the layers window will add a black filled mask to the current layer.
I use masked dupe screen and multiply layers to adjust most photos I edit and simply created an action linked to a function key to create them.
Thanks, I use that black mask sometimes, but was hoping there's a shortcut for adding a layer mask. In PS prefs, can't select a shortcut for some reason...
