Popular stencils
Microsoft Azure
This is a Stencil for Microsoft Azure Cloud Platform based on icons shared by on David Pallmann. Hope this helps someone. http://davidpallmann.blogspot.ca/2011/09/windows-azure-design-pattern-icons.html
Database Logos
I frequently find I use logos when diagramming infrastructure and application architectures. These logos are a preliminary set of the ones I find I use most commonly for databases. Feel free to request or recommend additions.
Physics Properties
Symbols to denote properties of physics.
Simple layered Architecture
a Simple Architecture
Military Symbols II
This is the second of two stencils of military (NATO) symbols I made and use for my wargames maps and orders of battle. I created it by scanning an existing chart and then converting it into vectors.
ArchiMate: Relations
This stencil is part of a set of ArchiMate stencils. ArchiMate is an enterprise architecture modelling language. Please note that to use the ArchiMate trademark commercially you also require an associated ArchiMate license.
Finger gestures for mobiles V1.0
Pointers and finger gestures for designing mobile experiences. You can use this stencil for designing UX (user experience), UI (user interaction), or interface design for mobiles.
Mac OS X Stencil
Mac OS X user interface components from the Mac OS X Stencil Kit.
Cisco CVD 2014 Collaboration Icons
Cisco released updated CVD Icons in many formats, but of course, no Omnigraffle stencil. These are built from the PNGs. http://www.cisco.com/c/en/us/solutions/enterprise/design-zone-smart-business-architecture/cvd.html This is the Collaboration Icons section.