On February 18, 2013, Microsoft released SQL Server 2008 R2 Service Pack 2 Cumulative Update 5, which is Build 10.50.4276. There are 21 fixes in the public fix list for this cumulative update, which is a pretty decent amount of fixes. This cumulative update is only for SQL Server 2008 R2 Service Pack 2. 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 2:
If you are running SQL Server 2008 R2, you should be on Service Pack 2 (at least in my humble opinion). If you are on SQL Server 2008 R2 Service Pack 2, you should make an effort to get the planning and testing infrastructure in place so that you can stay current with cumulative updates (rather than simply waiting for new service packs). I know that some organizations are completely against this philosophy, so I am going to make the case for my approach in an upcoming blog post.