The Feature Pack for Microsoft SQL Server 2008 R2 was released for download earlier this week, and includes PowerPivot for Excel 2010, as well as Report Builder 3.0!
The stand-alone download package for Report Builder 3.0 is available here: http://www.microsoft.com/downloads/details.aspx?FamilyID=d3173a87-7c0d-40cc-a408-3d1a43ae4e33
You can read about several of the new features and scenarios enabled with Report Builder 3.0 and RDL Version 2010, and take a look at the documentation overview for the latest version of Report Builder.
Enjoy and Happy Reporting!