Internet Explorer 9 Release Candidate can be downloaded at http://www.beautyOfTheWeb.com or at http://windows.microsoft.com/en-US/internet-explorer/downloads/ie.
OS supported are: Windows Vista/Windows 7/Windows Server 2008/Windows Server 2008 R2. There are already many languages available.
Finally the old known display mode for XML is back! (see my article: Internet Explorer 9 Beta does not display XML files in tree view ).
The site http://www.beautyOfTheWeb.com offers interesting information about new features and development tools for IE9.
Additionally there are advertised some featured sites tuned/created for IE9. One of my famous sites is BeatKeep: http://www.beatkeep.net/ - online music editor for (hobby) musicians.