Here's a few Rack Symbols that I've created over the last few years. Some are gear-specific. Some are generic. It works if you work in real-size, i.e. the racks are 19" wide in Omnigraffle, and your grid is 1.75" (a rack space).
This is a year stencil for use as a block in a timeline.
This is a compliation of twenty-one generic servers most of which are vendor neutral.
A stencil just for fun, including pac-man, the four ghosts and a scared ghost.
A Stencil with ordinary UML Use Cases with some color added. Note: This stencil uses the Omnigraffle Pro Subgraph feature.
Hydraulic power sources and components
Basic connections found on audio mixers.
I've used the cross functional diagram and this stencil several time to analyze the organization of different sized enterprises (SMEs and Big enterprises) for my consultancy work. It works well to define the organizational flow and to understand critical points within the organization.
Cable connectors and Jacks for Audio Visual Design and Network Designs