Microsoft has finally (after releasing the CTP version way back in April) released the final, gold build of SQL Server 2008 R2 SP1. This service pack includes the fixes from SQL Server 2008 R2 RTM Cumulative Updates 1 through 6, plus some new features that are not included in those Cumulative Updates. A TechNet Wiki with Release Notes for SQL Server 2008 R2 SP1 is available here.
If you have already installed SQL Server 2008 R2 RTM CU7 or CU8, you should hold off on installing SQL Server 2008 R2 SP1 until SQL Server 2008 R2 SP1 CU1 is released (probably in about six weeks), since that will probably be synchronized with SQL Server 2008 R2 RTM CU9, if history is any judge. If you are still on build 10.50.1600 or an earlier CU than CU7, you can go ahead and install Service Pack 1. The little build chart below might make it more clear.
— SQL Server 2008 R2 Builds SQL Server 2008 R2 SP1 Builds
— Build Description Build Description
— 10.50.1092 August 2009 CTP2
— 10.50.1352 November 2009 CTP3
— 10.50.1450 Release Candidate
— 10.50.1600 RTM
— 10.50.1702 RTM CU1
— 10.50.1720 RTM CU2
— 10.50.1734 RTM CU3
— 10.50.1746 RTM CU4
— 10.50.1753 RTM CU5
— 10.50.1765 RTM CU6 —> 10.50.2500 SP1 RTM
— 10.50.1777 RTM CU7
— 10.50.1797 RTM CU8
Also, don’t forget that none of this has anything to do with SQL Server 2008 (which is a separate older, major release according to Microsoft).