Mac OS X Keyboard Shortcut

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 10.2 and later)
Press Command-V during startup Start up in Verbose mode.
Start up in Single-User mode Start up in Single-User mode

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
(Assigned in Keyboard & Mouse preferences) Show Package Contents (of selected file in Mac OS X 10.5 or later only). To create this contextual menu shortcut, open Keyboard & Mouse preferences in Mac OS X 10.5, click Keyboard Shortcuts, click the "+" button, choose Finder.app as the Application, and type "Show Package Contents" (exactly), and set whichever shortcut you want, such as Command-Control-S.

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 (Mac OS X 10.2.8 or earlier), Add to Sidebar (Mac OS X 10.3 or later—use Shift-Command-T for 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
Option-Command-M Window Menu
     Minimize All Windows
Command-? Help Menu
     Open Mac Help
Command-Space Open Spotlight (Mac OS X 10.4 or later)
Command-esc Front Row
     Activates Front Row for certain Apple computers

Other Commands

Option-Command-D Show/Hide Dock
Command-Tab Switch application
tab Highlight next item
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
Shift-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 (dependant 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 (portables only--PowerBook, iBook, MacBook, MacBook Pro) Forward Delete (delete the character to the right of your cursor)

This list was created based on Apple document