Some featured white papers on the Exchange TechNet site:

 

Technical White Papers for Exchange Server 2010 

 

White Paper: Understanding the Relative Costs of Client Access Server Workloads in Exchange Server 2010

http://technet.microsoft.com/en-us/library/ff803560.aspx 

 

White Papers: Exchange 2010 Tested Solutions

http://technet.microsoft.com/en-us/library/gg513520.aspx

 

Cheers,

Rhoderick