If you want to make thumbnails of a web site shrinktheweb is a free web tool that will help you to make thumbnails in 6 different sizes. It is very simple and easy to use anybody.
To create simply type URL in shrinktheweb web site and click button then the thumbnails will appear in different sizes. The sizes include 75×56 90×68 100×75 120×90 200×150 and 320×200.If you ready to pay premium account you will get more options.