CTP has been made available earlier this week for SQL Server 2008 SP3 on Download Center. Read this MSDN blog post to get highlights of what has been updated.
Download Links :
SQL Server 2008 SP3 CTP : http://go.microsoft.com/fwlink/?LinkId=226850
SQL Server 2008 SP3 Express CTP : http://go.microsoft.com/fwlink/?LinkId=226851
SQL Server 2008 SP3 CTP has cumulative updates up to SP2 cumulative packages 1, 2, 3 and 4 and other reported issues from customer feedback. A list of bugs that are fixed in SQL Server 2008 Service Pack 3 CTP is available in KB Article 2546945 (http://support.microsoft.com/kb/2546945).
Note: There are some known issues with this SP3 CTP and TFS 2010 SP1.