Aruba Networks - Visio Stencils
Cisco Systems - Visio Stencils
VisoCafe - IBM's Visio collection see also developerWorks: Blogs - Nicolette's Random Musings - IBM Visio Stencil Library
IBM XIV Visio Diagrams see also Aussie Storage Blog - Storwize V7000 Visio Stencil
Juniper Networks - Product Icons and Visio Stencils
Technodrone - My Visio stencils again VMware stencils.
Dell Visio Stencils