Interclue is a Firefox extension that lets you preview whatever a hyperlink on a page is pointing to. Unlike other link previewers, Interclue doesn't just display a tiny replica of what's hiding under the link. It uses algorithms to intelligently construct a summary of the target page and displays it in a window with lots of other information and statistics about the page.
Essentially the goal of a link previewer is to save you clicks. But the way Interclue has been designed, it saves you a lot of time as well. It not only allows you to preview the link but also offers options to use the link itself in a variety of ways -- you can bookmark it in your browser and at del.icio.us, email it, or Digg it. If it's pointing to a Flickr image or a YouTube video, you can see the image or watch the video from within the preview window itself.