The Mango Windows Phone Developer Tools Windows Phone SDK Beta2 released today (the tools have been renamed to SDK). With the beta2 release you will see some additions to the tools like the Isolated Storage Explorer, improvements to the profiler and emulator as well as numerous updates to the docs. You can get the Mango beta2 tools on the download site, and see the changes to the documentation on MSDN.
Additionally, if you are already a registered Windows Phone developer, you should get an invitation to install the Mango bits on one registered device. You can see the details of this on the Windows Phone Developer Blog.