We absolutely *love* this free program from Wisdomsoft - we use it for everything from grabbing screen shots of video files, sending sample pics, of an in-progress site design to taking the final image for use in our portfolio.
It's great for measuring a space on a site as well, as you can stretch the marker tool across any part of the screen to check the exact number of pixels.
The uses are endless, and it's free which makes it even better!
Get the latest Screenhunter (version 5) here
UPDATE: CHECK FOR THE LATEST VERSION OF THIS DOWNLOAD AT THE LINK ABOVE - it has loads of new features INCLUDING the 'live browser recording' similar to JingProject!!