As the tast of browser testing is something that plagues all web designers, I thought I’d put together a short run-down of the currently available solutions. However, there is no definitive answer.
First off, Microsoft’s new SuperPreview sounded good, but this restricts you to IE 6 and the browser you currently have installed, such as IE 7 or IE 8, but not all three at the same time. May be a good solution if future updates included more browser options and live usage of the site in question rather than simple screenshots.
If you can suffice with screenshots and don’t need to test usability and interaction, then services such as browsershots.org, netrenderer and the recently released Alkaline application from Litmus are well worth looking at.