The Cumulative update package 13 for SQL Server 2008 R2 (Build 10.50.1815.0) is available:
http://support.microsoft.com/kb/2679366/
And here you can get the whole information of builds that were released after SQL Server 2008 R2 was released:
http://support.microsoft.com/kb/981356/
I wish you a nice day,
tosc