SiteShoter is a free standalone portable tool for Windows that can take screenshot of any website instantly and save it to an image file. All you have to do is enter the website URL, select the output destination, set some web browser options, and select the image size and quality.
You can also save the configuration, so that you can load it next time and save the headache of having to type all values again. It works on Windows XP, Windows 2003 Server, and Windows Vista. Enjoy!