Quickly take a window screenshot in Mac OS X
From Apple’s Pro Tips:
Hold down the Command, Shift, and 4 keys, then press the Spacebar. Instead of a cross-hair cursor, a small camera icon appears. When you move this camera icon over the element you’d like to capture, that element is highlighted. Click your mouse or trackpad, and you’ve captured a screenshot of just that element — no further cleanup required.
I knew about Command+Shift+4 and use it all the time, but I never knew about the spacebar trick to capture a particular window or element on the screen.
