http://browsershots.org/

In an ideal world, all web browsers would be 100% standards compliant, and the user’s choice of operating system would be immaterial. Unfortunately, web developers working in the real world know this is not the case. Most developers thus build in one browser, and test in as many as they can: this can often be time consuming, and requires multiple real or virtual machines. Browsershots makes testing across a range of browsers and OSs simple: simply choose the systems and versions you wish to test, enter the address of your site and press Submit.