Microsoft has released Cumulative Update 5 for SQL Server 2008 Service Pack 2. This CU has ten fixes listed in the knowledge base article, and it is Build 10.0.4316. This Cumulative Update is only for SQL Server 2008 SP2 (not for SQL Server 2008 R2).
Microsoft has also released Cumulative Update 15 for SQL Server 2008 Service Pack 1, with only four fixes listed in the KB article. This is Build 10.0.2847. Of course, it should not be a big surprise that I think you should be on the SQL Server 2008 SP2 branch by now. At some point, Microsoft will “retire” the SQL Server 2008 SP1 branch, making it an “unsupported service pack”.
Here is an updated SQL Server 2008 Build Chart that makes it a little easier to understand:
-- SQL Server 2008 RTM is considered an "unsupported service pack" as of April 13, 2010
-- SQL Server 2008 RTM Builds SQL Server 2008 SP1 Builds SQL Server 2008 SP2 Builds
-- Build Description Build Description Build Description
-- 1600 Gold RTM
-- 1763 RTM CU1
-- 1779 RTM CU2
-- 1787 RTM CU3 --> 2531 SP1 RTM
-- 1798 RTM CU4 --> 2710 SP1 CU1
-- 1806 RTM CU5 --> 2714 SP1 CU2
-- 1812 RTM CU6 --> 2723 SP1 CU3
-- 1818 RTM CU7 --> 2734 SP1 CU4
-- 1823 RTM CU8 --> 2746 SP1 CU5
-- 1828 RTM CU9 --> 2757 SP1 CU6
-- 1835 RTM CU10 --> 2766 SP1 CU7
-- RTM Branch Retired --> 2775 SP1 CU8 --> 4000 SP2 RTM
-- 2789 SP1 CU9
-- 2799 SP1 CU10
-- 2804 SP1 CU11 --> 4266 SP2 CU1
-- 2808 SP1 CU12 --> 4272 SP2 CU2
-- 2816 SP1 CU13 --> 4279 SP2 CU3
-- 2821 SP1 CU14 --> 4285 SP2 CU4
-- 2847 SP1 CU15 --> 4316 SP2 CU5 
