Hold the Option key while tapping the bright/dim buttons on the keyboard and the Displays preference pane pops up. So cool.
Bring back the power button's old behavior-- get a dialog box asking whether you want restart, shutdown, sleep, or cancel.
Delete an item from the keyboard! You'd think you'd use the Delete key, but you'd only be half right. The other half involves the Command key.
There's more than one way to do this, but Get Info does reveal the size of an image, in pixels. Rather handy. Try it!
If you're looking at a Finder window, and you want to go up one level to the folder that encloses the current one, this is the shortcut for you.
Mac users, if you know only four keyboard shortcuts, let them be these four! Command-Z, Command-X, Command-C, and Command-V are what make the Mac the Mac.
In a spreadsheet, tabbing goes forward... but Shift-tabbing goes backward! Also works in dialog boxes and web forms.
If your Mac's screen is white text on black, instead of black text on white, you may be in "Inverted" screen mode. Here's how you toggle that on and off.
Quit mousing around! Tap the "Esc" key (Escape) whenever you want to click a "Cancel" button. Quick and easy, never fails.