Mac OS X has a variety of built in screenshot methods. Here's a look at a few that offer more versatility than the basic full-screen capture (Command-Shift-3):
• Press Command-Shift-4 and you'll get a crosshair cursor with which you can drag to select and capture a certain area of the screen.
• Press Command-Shift-4-Space to select the entire window that the cursor is over, clicking on the window will then capture it. The resulting screenshot will even get a nice drop shadow.
• Hold down the Space bar after dragging out a selection window to move your selection rectangle around on the screen.
• Hold down Shift after dragging out a selection to constrain the selection in either horizontal or vertical orientation, depending on the direction of your drag.
• Hold down Option after dragging out a selection to expand the selection window around a center point.
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