Popular stencils
OpenStack
OpenStack is a cloud operating system that controls large pools of compute, storage, and networking resources throughout a datacenter, all managed through a dashboard that gives administrators control while empowering their users to provision resources through a web interface.
Simple Architecture
A stencil for Simple Architecture.
Degree Wheel
This symbol is a degree wheel or protractor. There are 360 ticks.
Constellation 1
A collection of astrological signs. (Part 1)
Physics Properties
Symbols to denote properties of physics.
Search (Magnolia CMS)
Search Paragraphs stencil from the Magnolia CMS Standard Templating Kit (STK) 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.
Rack Mount UPS
Several rack mount UPS systems
Facebook Stencil
Facebook user interface components from the Facebook Stencil Kit.