This is a terrific open source tool for Web designers: Browsershots (Inactive as of 2011)
Browsershots makes screenshots of your web design in different browsers. It is a free open-source online service created by Johann C. Rocholl. When you submit your web address, it will be added to the job queue. A number of distributed computers will open your website in their browser.
They make screenshots of your site in all the browsers you select for Linux, Windows, Mac OS, Gecko, and KHTML/WebKit and upload them to their central server.