The Cumulative update package 6 for SQL Server 2008 R2 Service Pack 1 (Build 10.50.2811.0) is available:
http://support.microsoft.com/kb/2679367/
And here you can get the whole information of builds that were released after SQL Server 2008 R2 Service Pack 1 was released:
http://support.microsoft.com/kb/2567616/
I wish you a nice day,
tosc