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Office 365 - Visio Stencils/Shapes for Online Services servers etc. by John_Palmer_Citrius
Microsoft has created an Exchange 2010 SP1 Visio Stencil as well as a Lync 2010 Stencil. Between those and the OOTB stencils you should have everything.
Microsoft Exchange 2010 Visio Stencil - http://www.microsoft.com/en-us/download/details.aspx?id=6977
Lync Server 2010 Visio Stencil - http://www.microsoft.com/en-us/download/details.aspx?id=20891
Update: January 2013
New Office Visio Stencil for Microsoft Office or Microsoft Office 365 deployments including Microsoft Exchange Server 2013, Microsoft Lync Server 2013, and Microsoft SharePoint Server 2013 are available at Download Center: New Office Visio Stencil