After releasing SQL Server 2008 R2 SP3 earlier in the month, Microsoft followed up with the release of the final service pack for the first revision of SQL Server 2008.
SQL Server 2008 SP4 include s a rollup of all 17 updates released for SQL Server 2008 SP3 (listed here). According to a Microsoft blog entry, any updates moving forward will not include functional fixes. While this marks the end of cumulative updates, Microsoft will continue to provide security updates as needed and within the guidelines of its mainstream and extended support policies.
For details and download information on SQL Server 2008 R2 SP3, go here. For SQL Server 2008 SP4, go here