WordPress.org

WordPress.com has a service called mShots that allows you to easily insert screenshots of any website into your blog. This simple plugin lets you use mShots with a shortcode.

Example Usage:

[mshot url="http://wpforchurch.com" alt="WordPress plugins and themes for churches and ministries" w="600" h=""300"]

This will generate a screenshot (that gets updated automatically). The image will link to the url in a new window.

Images will not always display instantly. Some take longer than others, but they'll show up eventually.

The idea and code for this plugin comes from here: http://www.wprecipes.com/wordpress-shortcode-display-a-thumbnail-of-any-website/