I always forget these:

  • 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

You can also change where your screenshots are saved:

defaults write com.apple.screencapture location ~/Pictures/Screenshots/

SOURCE:

http://guides.macrumors.com/Taking_Screenshots_in_Mac_OS_X