Useful Mac has awesome tips on taking screenshots with OS X built-in keyboard shortcuts.
I already knew about Command+Shift+3 for the whole screen and Command+Shift+4 for a selection of the screen. What I did not know were the options for scaling and free-move selection area. Really helpful if you take a lot of screenshots.
He also has a Terminal command to save the screenshots someplace else (Desktop is the default).
I would definitely subscribe to Useful Mac to your RSS feed if you like this type of stuff.