One stop shop for avoiding the confusing maze of Microsoft support links to get all the required hot fixes and updates to install Exchange 2010 SP1.
I typically download all the updates and divide them into 3 different ZIP files. 2008-R1.zip for all Server 2008 R1 hot fixes. 2008-R2.zip for all Server 2008 R2 hot fixes. Shared.zip for all the updates that are shared on both platforms. Very handy to keep on a USB thumb drive.
The only updates in the list that are not a deployment blocker by the Exchange 2010 SP1 setup program are the Server 2008 R2 WMI memory leak hot fixes - KB 977357 and 981314. If you monitor your Exchange servers with System Center Operations Manager or anything that repeatedly polls the WMI Win32_Service class, this hot fix is recommended.
From time to time, Microsoft updates the hot fixes. You can see that a few of the hot fixes are already on v2.
The upcoming service packs for Windows and .NET Framework will reduce the importance of these updates and will render the collection obsolete.