Popular stencils
Media Space
Tables, chairs, and media board objects (from the Media Computing Group).
Android 4 Tablet Stencil
Android 4 Tablet user interface components from the Android Stencil Kit.
Neutrik BNC NBB75DFIB chassis mount
Neutrik BNC NBB75DFIB chassis mount with drill order to scale
Oracle Servers & Storage '11
Some selection of current Oracle Sun Servers and Storage Systems
WindowsPhone 7 Controls
Replication of most of the controls for WindowsPhone 7. Probably could be optimized more but thought I'd share in the current state as it may be useful.
Wnt signal transduction components
Scientific cell biology / biochemistry depiction of core components of a cell-cell signalling pathway. The components allow diagrams to be rapidly generated illustrating features of the pathway.
Some basic network components
Various network components from various sources, some I've found useful over the years. I'm new to OmniGraffle, missed these items.
Clavister Security Gateway Series
This stencil contains a collection of Clavister Security Gateways for designing security network layouts.
Boyd Hobbs' Misc & Practical Lights
China Ball Lantern, Space Lights, Xenon, Airstar Balloon Lights, Bare Bulb, Lantern, Work Light, Flo Work Light, Lamp, Desk Lamp, Exit Sign, Emergency Light