On February 18, 2013, Microsoft released SQL Server 2008 R2 Service Pack 1 Cumulative Update 11, which is Build 10.50.2869. There are only four fixes in the public fix list for this cumulative update. This cumulative update is only for SQL Server 2008 R2 Service Pack 1. If you have a different version and/or service pack of SQL Server installed, the cumulative update will not install or work.

This KB article (which is a handy reference to bookmark) has links to all of the cumulative updates for SQL Server 2008 R2 Service Pack 1:

The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 Service Pack 1 was released