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WebDesignerWall has a big list of undocumented Photoshop shortcuts that you might find useful. Most notable are scroll wheel zooming by holding down Cmd+Opt, scroll wheel document panning by holding Cmd (or Cmd+Ctrl to toggle between left/right and up/down) and, my new favorite, moving a selection by holding the spacebar while dragging. The latter lets you reposition the top-left location of the marquee while you are still making it, which is about as useful as it comes when you are trying to select something to the exact pixel.

Photoshop Secret Shortcuts – Link