Snap an Idealab company located in Pasadena, California offers a product called Snap Preview Anywhere the ability to preview the links before you actually click them. I recently decided to add the feature to Somewhat Frank. With Snap Preview Anywhere links can be hovered over to display a thumbnail of the web site associated with the hyper-link. An example of the preview can be seen below.
Implementing the feature is a snap as you just need to add a snippet of code into your page or if you are a using WordPress you could leverage a WordPress Plug-in. Several sites are using the feature including TechCrunch, Monkey Bites and John Battelle's Search Blog - and now Somewhat Frank.