Mac OS X keyboard shortcuts

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.)
• Press Command-S during startup (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 Men 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))

Source: http://docs.info.apple.com/article.html?artnum=75459