Here’s a list of common Mac OS X keyboard shortcuts.

Startup
KeystrokesDescription
Press X during startupForce Mac to boot into Mac OS X when Classic is installed and set as the startup system.
Press Option-Command-Shift-DeleteBypass the startup disk set in the Startup Disk preference panel and boot from any other disk or volume with a viable Mac OS X operating system installed.
Press C during startupStart up from a CD or DVD that has a a viable system installed.
Press N during startupAttempt to start up from a compatible network server (NetBoot).
Press T during startupStart up in FireWire Target Disk mode.
Press Shift during startupStart 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 startupStart up in Verbose mode.
Press Command-S during startupStart up in Single-User mode.
Finder
KeystrokesDescription
Command-WClose Window.
Option-Command-WClose All Windows.
Command-Right ArrowExpand Folder (list view).
Option-Command-Right ArrowExpand folder and nested subfolders (list view).
Command-Left ArrowCollapse Folder (list view).
Option-Command-Up ArrowOpen parent folder and close current window.
Menu Commands
KeystrokeDescription
Apple menu
Shift-Command-QLog out. Same as clicking Log Out… in the Apple menu. You’ll be asked if you want to quit all applications and log out.
Shift-Option-Command-QLog out immediately.
Finder menu
Shift-Command-DeleteEmpty Trash
Option-Shift-Command-DeleteEmpty Trash without dialog
Command-HHide Finder.
Option-Command-HHide Others.
File menu
Command-NNew Finder window.
Shift-Command-NNew Folder.
Command-OOpen.
Command-SSave.
Shift-Command-SSave as.
Command-PPrint.
Command-WClose Window.
Option-Command-WClose All Windows.
Command-IGet info.
Option-Command-IShow Attributes Inspector.
Command-DDuplicate.
Command-LMake alias.
Command-RShow original.
Command-TAdd 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-DeleteMove to Trash.
Command-EEject.
Command-FFind.
Edit Menu
Command-ZUndo.
Command-XCut.
Command-CCopy.
Command-VPaste.
Command-ASelect All.
View Menu
Command-1View as Icons.
Command-2View as List.
Command-3View as Columns.
Command-BHide Toolbar.
Command-JShow View Options.
Go Menu
Command-[Back.
Command-]Forward.
Shift-Command-CComputer.
Shift-Command-HHome.
Shift-Command-IiDisk.
Shift-Command-FFavorites.
Shift-Command-GGo to Folder.
Shift-Command-KConnect to Server.
Window Menu
Command-MMinimize Window.
Option-Command-MMinimize All Windows.
Help Menu
Command-?Open Mac Help.
Miscellaneous
Comand-SpaceOpen Spotlight (Mac OS X 10.4 and later).
Command-EscActivates Front Row for certain Apple computers