Fade the Last Filter Used

Menu: Filter Fade name of the filter

Mac: Cmd + Shift + F

Win: Ctrl + Shift + F

This is a great shortcut to knock back the intensity of a particular effect by playing with the opacity or the blend mode of the applied filter effect. In Photoshop 6 and 7, the Fade command can also apply to brush strokes and other edits. (In these versions, you'll find the menu item under the Edit menu.)