IE7 Beta 2 is now available for download.

There is also an Add-Ons site where you can find some cool tools that are screened by Microsoft and rated by users to help you select the ones that suit your needs and preferences.

The best developer add-on is not listed on this site, but comes directly from MS and works on IE6 too. You can download it at Developer Toolbar Download. This tool enables you to explore the DOM tree and find elements on the page, disable IE settings, view information, outline elements, control images, resize pages to common screen resolutions and have a powerful ruler that lets you measure pixel perfect content on your page.