MAC OS has many usefull shortcut commands and some of them are listed here below category-wise which can be used more frequently by the mac users. The list is bit long but usefull for mac users in general.
1) Startup
"Press X during startup" = Force Mac OS X startup
"Press Option-Command-Shift-Delete during startup" = Bypass primary startup volume and seek a different startup volume (such as a CD or external disk)
"Press C during startup" = Start up from a CD that has a system folder
"Press N during startup" = Attempt to start up from a compatible network server (netboot)
"Press T during startup" = Start up in FireWire Target Disk mode
"Press Shift during startup" = start up in Safe Boot mode and Temporarily disable login items and non-essential kernel extension files (Mac OS X February 10 and later)
"Press Command-V during startup" = Start up in verbose mode
"Press Command-S during startup" = Start up in Single-User mode
2) Finder window
"Command-W" = Close Window
"Option-Command-W" = Close all Windows
"Command-Right Arrow" = Expand folder (list view)
"Option-Command-Right Arrow" = Expand folder and nested subfolders (list view)
"Command-left Arrow" = Collapse Folder (list view)
"Option-Command-Up Arrow" = Open parent folder and close current window
3) Menu Commands
"Shift-Command-Q" = Apple Menu Log out
"Shift-Option-Command-Q" = Apple Menu Log out immediately
"Shift-Command-Delete" = Finder Menu Empty Trash
"Option-Shift-Command-Delete" = Finder Menu Empty Trash without dialog
"Command-H" = Finder Menu Hide Finder
"Option-Command-H" = Finder Menu Hide Others
"Command-N" = File Menu New Finder window
"Shift-Command-N" = File Menu New Folder
"Command-O" = File Menu Open
"Command-S" = File Menu Save
"Shift-Command-S" = File Menu Save as
"Command-P" = File Menu Print
"Command-W" = File Menu Close Window
"Option-Command-W" = File Menu Close all Windows
"Command-I" = File Menu Get Info
"Option-Command-I" = File Menu Show Attributes Inspector
"Command-D" = File Menu Duplicate
"Command-L" = File Menu Make Alias
"Command-R" = File Menu Show original
"Command-T" = File Menu Add to Favorites
"Command-Delete" = File Menu Move to Trash
"Command-E" = File Menu Eject
"Command-F" = File Menu Find
"Command-Z" = Edit Menu Undo
"Command-X" = Edit Menu Cut
"Command-C" = Edit Menu Copy
"Command-V" = Edit Menu Paste
"Command-A" = Edit Menu Select All
"Command-1" = View Menu View as Icons
"Command-2" = View Menu View as List
"Command-3" = View Menu View as Columns
"Command-B" = View Menu Hide Toolbar
"Command-J" = View Menu Show View Options
"Command - [" = Go Menu Back
"Command -]" = Go Menu Forward
"Shift-Command-C" = Go Menu Computer
"Shift-Command-H" = Go Menu Home
"Shift-Command-I" = Go Menu iDisk
"Shift-Command-A" = Go Menu Applications
"Shift-Command-F" = Go Menu Favorites
"Shift-Command-G" = Go Menu Goto Folder
"Command-K" = Go Menu Connect to Server
"Command-M" = Window Menu Minimize Window
"Command-?" = Help Menu Open Mac Help
"Command-Space" = Open Spotlight (Mac OS X 10.4 or later)
"Command-Alt-Space" = Open Spotlight Guide (Mac OS X 10.4 or later)
"F12" = Opens Dashboard (Mac OS X 10.4 or later)
Universal Access and Voiceover
"Option-Command-* (asterisk)" = Turn on Zoom
"Option-Command-+ (plus)" = Zoom in
"Option-Command - (minus)" = Zoom out
"Control-Option-Command-* (asterisk)" = Switch to White on Black
"Control-F1" = Turn on Full Keyboard Access
When Full Keyboard Access is turned on, you can use the key combinations listed in the table below from the Finder.
"Control-F2" = Full Keyboard Access Highlight Menu
"Control-F3" = Full Keyboard Access Highlight Dock
"Control-F4" = Full Keyboard Access Highlight Window (active) or next window behind it
"Control-F5" = Full Keyboard Access Highlight Toolbar
"Control-F6" = Full Keyboard Access Highlight Utility window (palette)
"Command-F5 or fn-Command-F5" = Turn on or off Voiceover (Mac OS X 10.4 or later)
"Control-Option-F8 or fn-Control-Option-F8" = Open Voiceover Utility (Mac OS X 10.4 or later)
"Control-Option-F7 or fn-Control-option-F7" = Display Voiceover menu (Mac OS X 10.4 or later)
"Control-Option-; or fn-Control-option-" = Enable / disable lock Voiceover Control-Option (Mac OS X 10.4 or later)
4) Mouse Keys
"8" = Move Up
"2" = Move Down
"4" = Move left
"6" = Move Right
"1, 3, 7, 9" = Move diagonally
"5" = Press Mouse Button
"0" = Hold Mouse Button
". (Period on keypad)" = Release Mouse Button (use after pressing 0)
5) Other Commands
"Option-Command-D" = Show / Hide Dock
"Command-Tab" = Switch application
"Command-Up Arrow" = Move up one directory
"Command-Down Arrow" = Move down one directory
"Page Up or Control-Up Arrow" = Move up one page
"Page Down or Control-Down Arrow" = Move down one page
"Option-Drag" = Copy to new location
"Option-Command-Drag" = Make alias in new location
"Command-Drag" = Move to new location without copying
"Command-C" = Show Colors palette in application
"Command-T" = Show Font palette in application
"Command-Shift-3" = Take a picture of the screen
"Command-Shift-4" = Take a picture of the selection
"Command-Shift-4, then press Control while selecting" = Take a picture of the screen, place in Clipboard
"Command-Shift-4, then Spacebar" = Take a picture of the selected window
"Option-Command-esc" = Force Quit
"Control-Eject" = Restart, Sleep, Shutdown dialog box
"Control-Command-Eject" = Quit all applications and restart
"Option-Command-Eject or Option-Command-Power" = Sleep
"Command-click window toolbar button (upper right corner)" = Cycle through available views for the window's toolbar (dependent on the nature of the Finder or application window)
"Command-` " = Cycle through windows in application or Finder (if more than one window is open)
"Function-Delete (PowerBook, iBook only)" = Forward Delete (delete the character to the right of your cursor)
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1) Startup
"Press X during startup" = Force Mac OS X startup
"Press Option-Command-Shift-Delete during startup" = Bypass primary startup volume and seek a different startup volume (such as a CD or external disk)
"Press C during startup" = Start up from a CD that has a system folder
"Press N during startup" = Attempt to start up from a compatible network server (netboot)
"Press T during startup" = Start up in FireWire Target Disk mode
"Press Shift during startup" = start up in Safe Boot mode and Temporarily disable login items and non-essential kernel extension files (Mac OS X February 10 and later)
"Press Command-V during startup" = Start up in verbose mode
"Press Command-S during startup" = Start up in Single-User mode
2) Finder window
"Command-W" = Close Window
"Option-Command-W" = Close all Windows
"Command-Right Arrow" = Expand folder (list view)
"Option-Command-Right Arrow" = Expand folder and nested subfolders (list view)
"Command-left Arrow" = Collapse Folder (list view)
"Option-Command-Up Arrow" = Open parent folder and close current window
3) Menu Commands
"Shift-Command-Q" = Apple Menu Log out
"Shift-Option-Command-Q" = Apple Menu Log out immediately
"Shift-Command-Delete" = Finder Menu Empty Trash
"Option-Shift-Command-Delete" = Finder Menu Empty Trash without dialog
"Command-H" = Finder Menu Hide Finder
"Option-Command-H" = Finder Menu Hide Others
"Command-N" = File Menu New Finder window
"Shift-Command-N" = File Menu New Folder
"Command-O" = File Menu Open
"Command-S" = File Menu Save
"Shift-Command-S" = File Menu Save as
"Command-P" = File Menu Print
"Command-W" = File Menu Close Window
"Option-Command-W" = File Menu Close all Windows
"Command-I" = File Menu Get Info
"Option-Command-I" = File Menu Show Attributes Inspector
"Command-D" = File Menu Duplicate
"Command-L" = File Menu Make Alias
"Command-R" = File Menu Show original
"Command-T" = File Menu Add to Favorites
"Command-Delete" = File Menu Move to Trash
"Command-E" = File Menu Eject
"Command-F" = File Menu Find
"Command-Z" = Edit Menu Undo
"Command-X" = Edit Menu Cut
"Command-C" = Edit Menu Copy
"Command-V" = Edit Menu Paste
"Command-A" = Edit Menu Select All
"Command-1" = View Menu View as Icons
"Command-2" = View Menu View as List
"Command-3" = View Menu View as Columns
"Command-B" = View Menu Hide Toolbar
"Command-J" = View Menu Show View Options
"Command - [" = Go Menu Back
"Command -]" = Go Menu Forward
"Shift-Command-C" = Go Menu Computer
"Shift-Command-H" = Go Menu Home
"Shift-Command-I" = Go Menu iDisk
"Shift-Command-A" = Go Menu Applications
"Shift-Command-F" = Go Menu Favorites
"Shift-Command-G" = Go Menu Goto Folder
"Command-K" = Go Menu Connect to Server
"Command-M" = Window Menu Minimize Window
"Command-?" = Help Menu Open Mac Help
"Command-Space" = Open Spotlight (Mac OS X 10.4 or later)
"Command-Alt-Space" = Open Spotlight Guide (Mac OS X 10.4 or later)
"F12" = Opens Dashboard (Mac OS X 10.4 or later)
Universal Access and Voiceover
"Option-Command-* (asterisk)" = Turn on Zoom
"Option-Command-+ (plus)" = Zoom in
"Option-Command - (minus)" = Zoom out
"Control-Option-Command-* (asterisk)" = Switch to White on Black
"Control-F1" = Turn on Full Keyboard Access
When Full Keyboard Access is turned on, you can use the key combinations listed in the table below from the Finder.
"Control-F2" = Full Keyboard Access Highlight Menu
"Control-F3" = Full Keyboard Access Highlight Dock
"Control-F4" = Full Keyboard Access Highlight Window (active) or next window behind it
"Control-F5" = Full Keyboard Access Highlight Toolbar
"Control-F6" = Full Keyboard Access Highlight Utility window (palette)
"Command-F5 or fn-Command-F5" = Turn on or off Voiceover (Mac OS X 10.4 or later)
"Control-Option-F8 or fn-Control-Option-F8" = Open Voiceover Utility (Mac OS X 10.4 or later)
"Control-Option-F7 or fn-Control-option-F7" = Display Voiceover menu (Mac OS X 10.4 or later)
"Control-Option-; or fn-Control-option-" = Enable / disable lock Voiceover Control-Option (Mac OS X 10.4 or later)
4) Mouse Keys
"8" = Move Up
"2" = Move Down
"4" = Move left
"6" = Move Right
"1, 3, 7, 9" = Move diagonally
"5" = Press Mouse Button
"0" = Hold Mouse Button
". (Period on keypad)" = Release Mouse Button (use after pressing 0)
5) Other Commands
"Option-Command-D" = Show / Hide Dock
"Command-Tab" = Switch application
"Command-Up Arrow" = Move up one directory
"Command-Down Arrow" = Move down one directory
"Page Up or Control-Up Arrow" = Move up one page
"Page Down or Control-Down Arrow" = Move down one page
"Option-Drag" = Copy to new location
"Option-Command-Drag" = Make alias in new location
"Command-Drag" = Move to new location without copying
"Command-C" = Show Colors palette in application
"Command-T" = Show Font palette in application
"Command-Shift-3" = Take a picture of the screen
"Command-Shift-4" = Take a picture of the selection
"Command-Shift-4, then press Control while selecting" = Take a picture of the screen, place in Clipboard
"Command-Shift-4, then Spacebar" = Take a picture of the selected window
"Option-Command-esc" = Force Quit
"Control-Eject" = Restart, Sleep, Shutdown dialog box
"Control-Command-Eject" = Quit all applications and restart
"Option-Command-Eject or Option-Command-Power" = Sleep
"Command-click window toolbar button (upper right corner)" = Cycle through available views for the window's toolbar (dependent on the nature of the Finder or application window)
"Command-` " = Cycle through windows in application or Finder (if more than one window is open)
"Function-Delete (PowerBook, iBook only)" = Forward Delete (delete the character to the right of your cursor)
