The first community technology preview (CTP) of Microsoft SQL Server 2008 R2 available for download for MSDN and TechNet subscribers.
For more details about SQL Server 2008 R2 and for other related links See - http://www.microsoft.com/sqlserver/2008/en/us/R2.aspx
If you have any questions regarding SQL Server 2008 R2 you can visit the forums - http://social.msdn.microsoft.com/Forums/en-US/category/sqlserverprerelease