How to pull a list of applied service packs and cumulative updates from SQL Server 2008 R2? I want to list all the SPs and CUs applied to a SQL Server 2008R2 instance.

Example: 


10.50.4260 2720425 http://support.microsoft.com/kb/2720425 CU#1 for SQL Server 2008 R2 SP2
10.50.4000 2630458 http://support.microsoft.com/kb/2630458 Service Pack 2 
10.50.2881 2868244 http://support.microsoft.com/kb/2868244 CU#14 for SQL Server 2008 R2 SP1


How can I get the above list from SQL Server 2008R2 instance?
Cumulative updates are exactly that, cumulative. CU2 for example contains all of the fixes included in CU1. As such, the only SP or CU that matters is the last one to be applied which you can determine with:

SELECT @@VERSION


and Google or a reference list of SQL Server versions. SQLServerBuilds is the popular unofficial list, KB321185 is the official list.

I'm not aware of any way to obtain a complete list of all patches that have ever been applied to an instance. It's likely buried in the registry somewhere but I haven't fished for it.