I have tested a lot of tools a site sites thumbnail generators to use with a pligg (digg style sms) site but I think that http://www.megasnaps.com
is the best for this use. His free web site to image page, create a image of the whole html page, and offers a cropped options too to be downloaded.
The website thumbnails generator service are a good option for any type of web sites, offers a full page and custom sizes for the cheaper price tha I have found. I do a great instalation with 'facebox' (jquery), by clicking on a small image it open a larger one 'facebook style' image with a full size snapshot looks great!.
hope it helps.