Keyboard Shortcuts

This isn't meant to be a comprehensive list, it's just a list of keyboard shortcuts I find useful but always have to look up.

Screenshots

Command-Shift-3: Take a screenshot of the screen, and save it as a file on the desktop
Command-Shift-4, then select an area: Take a screenshot of an area and save it as a file on the desktop
Command-Shift-4, then space, then click a window: Take a screenshot of a window and save it as a file on the desktop
Command-Control-Shift-3: Take a screenshot of the screen, and save it to the clipboard
Command-Control-Shift-4, then select an area: Take a screenshot of an area and save it to the clipboard
Command-Control-Shift-4, then space, then click a window: Take a screenshot of a window and save it to the clipboard

In Leopard, the following keys can be held down while selecting an area (via Command-Shift-4 or Command-Control-Shift-4):

Space, to lock the size of the selected region and instead move it when the mouse moves
Shift, to resize only one edge of the selected region
Option, to resize the selected region with its center as the anchor point

By default, screenshots are .png format. To change that, type this at a terminal:

defaults write com.apple.screencapture type image_format
killall SystemUIServer

where image_format is "png", "jpg", etc...

Press X during startup = Force Mac OS X startup
Option-Command-Shift-Delete = Bypass primary startup volume and seek a different startup volume (such as a CD or external disk)
C = Start up from a CD that has a system folder
N = Attempt to start up from a compatible network server (NetBoot)
T = Start up in FireWire Target Disk mode
Shift = start up in Safe Boot mode (temporarily disable login items and non-essential kernel extension files)
Command-V = Start up in Verbose mode
Command-S = Start up in Single-User mode

I forget how to do this, so every time I have to figure it out.

Divvy http://www.mizage.com/ - I only paid about $15 for this utility, and I now use it at least 70 times a day. It's hugely useful.