There's no shortage of apps for taking screenshots, many of them with annotation and other powerful features. However, web app Site2Pic is a stand-out for its simplicity. It does one thing and it does it well: take a screenshot of a web page for sharing.
Just enter the URL and you'll quickly get a downloadable snapshot of the web page plus a link to the image, good for posting on forums and comments on blogs, etc. That's about as easy as it gets.