The Finder performs most of the important functions within OS X Mountain Lion, and the following shortcuts will help you get things done more efficiently.

Key Function
Command+A Selects all items in the active window (icon view), all items in the column (column view), or all items in the list (cover flow view)
Command+C Copies selected items
Command+D Duplicates the selected item(s)
Command+E Ejects the selected volume
Command+F Displays the Find dialog
Command+H Hides All Finder windows
Command+I Shows info for selected item or items
Command+J Shows the view options for the active window
Command+K Displays the Connect to Server dialog
Command+L Creates an alias for the selected item
Command+M Minimizes the active window
Command+N Opens a new Finder window
Command+O Opens (or launches) the selected item
Command+R Shows the original for selected alias
Command+T Adds the selected item to the Sidebar
Command+V Pastes items from the Clipboard
Command+W Closes the active window
Command+X Cuts the selected items
Command+Z Undoes the last action (if possible)
Command+, Displays Finder Preferences
Command+1 Shows the active window in icon mode
Command+2 Shows the active window in list mode
Command+3 Shows the active window in column mode
Command+4 Shows the active window in cover flow mode
Command+[ Moves back to the previous Finder location
Command+] Moves forward to the next Finder location
Command+Del Moves selected items to the Trash
Command+Up Arrow Show enclosing folder
Command+` Cycles through windows
Command+? Displays the OS X Help Viewer
Command+Shift+A Takes you to your Applications folder
Command+Shift+C Takes you to the top-level Computer location
Command+Shift+G Takes you to a folder that you specify
Command+Shift+H Takes you to your Home folder
Command+Shift+Q Logs you out
Command+Shift+N Creates a new untitled folder in the active window
Command+Shift+U Takes you to your Utilities folder
Command+Shift+Del Deletes the contents of the Trash
Command+Option+H Hides all windows except the Finder's window(s)
Command+Option+N Creates a new Smart Folder
Command+Option+T Hides the Finder window toolbar and sidebar
Command+Option+Space Opens the Spotlight window
Command+Space Opens the Spotlight menu
Control+Up Arrow (or F3, depending on your keyboard model) Displays the Mission Control screen
Control+Down Arrow (or Control+F3, depending on your keyboard model) Shows all open windows for the current application using Mission Control
F11 (or Command+F3, depending on your keyboard model) Hides all windows to display the Desktop using Mission Control
F12 (or F4, depending on your keyboard model) Displays your Dashboard widgets
Space Quick Look