You can download it here. Check out Brandon Watson’s post for detail.
“When the Windows Phone 7 OS went gold two weeks ago, the Windows Phone ecosystem began the final preparations for the upcoming launch. OEMs and mobile operators have begun final testing of their handsets, but developers have had to wait just a little while longer to complete apps and games. Today, that wait is over. The Windows Phone Developer Tools have gone final, and we have released to the Web. This release is English only, but we will be releasing the French, Italian, German and Spanish language versions in the next couple of weeks.
“For developers to put their apps into the marketplace, opening in early October, you will need to download this version of the tools. Any application built with a previous version of the tools will fail application certification in the Marketplace. When you do submit your application, you can expect it to take about five days to pass or fail certification, though you can check the status of your app submission at any time at the developer portal. For more information on passing certification, please see the Windows Phone 7 Marketplace policies.