⌘+shift + i inverts the current selection
⌘+⌥+Z gives you an undo as man times as your history will allow.
⌘+Shift +E merges all visible layers
⌥ +shift + ⌘ + K brings up a list of all photoshop keyboard shortcuts.
⌘ + K brings up the preferences menu
⌘+ shift +S does a save as on the current document
⌘+ ⌥ +shift+S brings up the menu to save the current document for the web
⌘+ F re-applies the last filter that you applied to the current document
⌘+ L brings up your levels adjustment menu
⌘ +M brings up the curves adjustment menu
⌘ + U brings up your hue/saturation adjustment menu
⌘ + B brings up your color balance adjustment menu
Shift + ⌘ + U desaturates your image, removing all color information from the document
⌘+J Makes a new layer copy of the current layer
Shift + ⌘ + N makes a new layer
