Very early this morning, Microsoft released four updates: one for SQL Server 2005 SP3, one for SQL Server 2005 SP4, one for SQL Server 2008 SP1, and one for SQL Server 2008 SP2.
Cumulative Update KB Article Build Number Number of Fixes SQL Server 2005 SP3 Cumulative Update #15 KB #2507766 9.00.4325 6 SQL Server 2005 SP4 Cumulative Update #3 KB #2507769 9.00.5266 5 SQL Server 2008 SP1 Cumulative Update #13 KB #2497673 10.00.2816 12 SQL Server 2008 SP2 Cumulative Update #3 KB #2498535 10.00.4279 25
Note that Microsoft has officially confirmed that these are the last cumulative updates for SQL Server 2005 (both SP3 and SP4). So if you're still on SQL Server 2005, it really is time to start considering how long you want to stay on that platform.
Also, please do not try to apply the SQL Server 2008 cumulative updates to SQL Server 2008 R2 systems. You won't get very far and you won't break anything; I'm just trying to save you some time.