For Windows Users: Use IETester (
http://www.my-debugbar.com/wiki/IETester/HomePage) to view the page in all IE versions from 5.5 up to 8. (by now) This tool does NOT make Screenshots, it shows the page working!
To have a short look on how the page looks like in other browsers, try
http://browsershots.org/ This service creates screenshots. It's enough to see if a page is completely broken in exotic browsers or good enough for all of them.
