Microsoft has released SQL Server 2008 Service Pack 3 Cumulative Update 9, which is build 10.00.5829. As you might expect from the build number (which is only one number higher than SQL Server 2008 Service Pack 3 Cumulative Update 8), there are very few fixes in the public fix list. Three to be exact.
There is no corresponding Cumulative Update for SQL Server 2008 RTM, SP1, or SP2, since those service pack levels are retired. SQL Server 2008 RTM was retired on April 13, 2010, SQL Server 2008 SP1 was retired on September 19, 2011, and SQL Server 2008 SP2 was retired on September 17, 2012.
Many people seem to be surprised to hear this, but I see systems on SQL Server 2008 SP1 or older all the time. If you are running SQL Server 2008, you really should be on Service Pack 3 by now. I would be surprised if Microsoft is going to release a SQL Server 2008 Service Pack 4.
Mainstream support for both SQL Server 2008 and 2008 R2 is still scheduled to end on January 14, 2014.