Holding down Option and Pressing Escape works, too.

So, for example, if you type create, you get a list of words including create, created, and creates.

If there are a lot of words in the list, it only shows the first 100 results, sorted alphabetically. The results come from Mac OS X’s built-in dictionary.

This trick is useful for when you have a word on the tip of your tongue, need help with possessive apostrophes, or are stuck on a crossword clue.

It’s a pretty long list, but perhaps useful..

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

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 VoiceOver on or off (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 VoiceOver Control-Option lock (Mac OS X 10.4 or later)

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)

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 (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 (PowerBook, iBook only)” = Forward Delete (delete the character to the right of your cursor)

Pretty long list =)

Source: The Apple Support Page

Open System Preferences, and then click Security.
Select “Require password to wake this computer from sleep or screen saver.”
A person with an administrator account can use their name and password to unlock the screen.

Locking the screen does not prevent other users from turning off the computer and restarting it, then logging in to their own account. If you think this could happen, be sure to save your work before you leave your computer.

If your computer has multiple users and you want more than one user to stay logged in at a time, select “Enable fast user switching” in the Accounts preferences. To lock your screen quickly with fast user switching enabled, choose Login Window from the menu with your username. You applications will remain open and undisturbed but your computer will be locked.

Press X during startup:
Force Mac OS X startup

Press Option during startup:
Select startup drive using graphical interface

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 R during startup:
Force PowerBook screen reset

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