Tools for Checking a Website's Browser Compatibility

In the spirit of a great debate regarding the proposed death of Internet Explorer 6 (IE6) over at the about.com Web Design Blog (article found here), I have decided to post a few useful tools for checking a website's browser compatibility. I must say that I strongly support the adoption of newer, better web browsing standards, and it is definitely time for IE6 users to upgrade.

1. MultipleIEs - Allows user to install old versions of Internet Explorer, 3.0 up to 6.0. Unfortunately, it does not work in Windows Vista. Free.
2. IE NetRenderer - A very nice online tool that will take a screen shot of the URL of your choice using IE 5.5, 6.0, 7.0, and 8.0. Free.
3. BrowserShots.org - Probably the most well-known of all the cross-browser testing websites, it supports an amazing amount of browsers, browser versions, and many operating systems (Unix, Windows, Mac OS, BSD). Offers free and a priority (paid) service at $29.95/month.
4. CrossBrowserTesting.com - The most comprehensive cross-browser testing tool. Very cool how it works. Neat pay-as-you-go credit system. First 5 minutes free.
   

Have another to add to this list? Post it in a comment!