Here are some Visio stencils from different vendors to use for making a diagram for Citrix,  RES, Microsoft and VMware. See the links below.

 

 

 

 

 

 

Citrix Visio Stencils (XenApp, VDI, Netscaler, XenDesktop, EdgeSight, Access Gateway, Citrix Delivery Center items, Roles)
http://blogs.citrix.com/2010/10/12/citrix-networking-visio-stencil-set/

RES Automation Manager + Workspace Manager +  Service Orchestration Visio Stencils
https://support.ressoftware.com/Modules/Downloads/DownloadsTreeView.aspx?downloadguid=a30a55c4-48ae-e111-a829-005056bb474c

Microsoft Hyper-V, SCVMM Stencils
http://gallery.technet.microsoft.com/Hyper-VSCVMM-Vision-Stencil-3dc18770/file/45652/1/Virtualization_Modern.vss

Microsoft Datacenter template
http://visio.microsoft.com/en-us/Samples_and_Downloads/Diagrams_and_Templates/Pages/Data_Center.aspx

Lot of shapes / stencils of Microsoft
http://visio.microsoft.com/en-us/Samples_and_Downloads/Diagrams_and_Templates/Pages/default.aspx?Filter1=Sample+Diagram+Templates%7ca37176ad-3309-4715-a814-37c68e08f729%3bDiagrams+and+templates%7cb21839e4-b8a2-458d-8538-7e99e23a90ed

VMware stencils
http://communities.vmware.com/servlet/JiveServlet/download/11498-6-60388/VMware-Stencil2-vSphere.zip

http://communities.vmware.com/servlet/JiveServlet/download/11498-6-60389/VMware-Stencil1-vSphere.zip