janrenz

With Usage of the wordpress.com inofficial webpage to screenshot function this plugins generates screenshots of websites. For more information check http://bdisco.de/wordpress-plugins/ 
There are a few options you can use in your shortcode [webscreenshot]:
url: full Url of the webpage which you want to have screenshoted (mandantory)
width: Pixel width of the screenshot (optional, default: 250)
refresh: If you want to reload the screenshot if it wasn’t generated on the first call (optional, default: true)
link: link image to given url (optional, default: true)
newpage: open link in new page (optional, default: true)
title: set link title tag (will be used as img alt tag also) (optional, default:”)
All img-tags generated will have a class called “webscreenshot”, the link will have a class called “webscreenshot-link” which you can you to perform additional style stuff
Feel free to make pull requests at https://github.com/jprberlin/web-screenshots

Web Screenshots

Displays Thumbnails of a given URL usings wordpress.com inofficial API. Use Shortcode [webscreenshot] with url and some  optional params.

Thomas Schulte

This plugin dynamically shows preview screenshots of hyperlinks as tooltips on your WordPress site.
For the tooltip effect a jQuery plugin called “qTip2” is used internally. 
Find more about this great project here: http://qtip2.com/ 
The thumbnails are provided by http://thumbsniper.com and its API.

ThumbSniper

This plugin dynamically shows preview screenshots of hyperlinks as tooltips on your WordPress site.

Web Screenshots vs ThumbSniper