Photoshop’s Edit>Free Transform command (Command-T) offers some additional keyboard shortcuts for "step-and-repeat" functions that can be very useful:

To make the same transformation again, for an additive effect or with a different layer targeted, Transform Again by pressing Command-Shift-T.

To make a new copy and transform the copy, press Command-Option-Shift-T.

Add, Take Away, or Intersect a Selection

You can Command-click on a path, channel, or layer to load it as a section. Hold shift to add an active selection, Option to take away and Shift-Option to intersect it.

Add a Layer below the Active Layer

Command-click the New Layer icon at the bottom of the layers palette to add a layer below the active one.

All-change mode

Hold Shift when clicking the Full-Screen Mode icon at the bottom of the Toolbox to change the mode of all the open documents.

Cycle through all open documents

Press Control-Tab multiple times to cycle through all of the documents that are currently open.

Reset Character

Photoshop CS remembers whatever settings you last used to format type. To quickly reset Photoshop’s type to its "default" standard settings, just go to the Character palette, and choose Reset Character from the palette’s pop-down menu.