A handy set of isometric icons based on Visio's icons.
Stencil of additional Apple hardware and misc. networking components. Excellent for creating physical diagrams.
Stencils for QLogic Fibre Switches
Voice, VoIP and other related devices.
The MacADSL team has designed a network stencil that can be used to draw networks in a comprehensive way with few colors in order to generate small image files to be published on the web.
Firewalls, VPNs, etc.
Collection of hosts, clients and assorted support.
The following picture shows an OmniGraffle palette I put together for doing network diagrams. It may be useful for others.
WLANs, RF, etc.