In addition to SQL Server 2008 R2 SP1 CU1, Microsoft today also released cumulative updates for the SQL Server2008 branches (Service Pack 1 and Service Pack 2). You can download these updates from the following KB articles:
KB #2555406 : Cumulative update package 15 for SQL Server 2008 Service Pack 1
(Build number = 10.00.2847)
KB #2555408 : Cumulative update package 5 for SQL Server 2008 Service Pack 2
(Build number = 10.00.4316)
And if you want to slipstream one of these CUs with its associated base service pack, you can follow Peter Saddow's instructions here (the specific file names are different, but the concept is exactly the same):
To be clear…
As a reminder, these cumulative updates are only for SQL Server 2008 SP1 (10.00.2531 -> 10.00.2846) and SP2 (10.00.4000 -> 10.00.4315), not for SQL Server 2008 RTM (10.00.anything less than 2531) or for SQL Server 2008 R2 (version 10.50.anything).