Network stencils
OS logos
A collection of OS/hardware logos, including Sun, HP, Linux, Red Hat, FreeBSD, Windows, Debian, Darwin, IBM, and VMware.
Isometric icons
A handy set of isometric icons based on Visio's icons.
Apple Elements
Stencil of additional Apple hardware and misc. networking components. Excellent for creating physical diagrams.
QLogic Switches
Stencils for QLogic Fibre Switches
Cisco Stencils (Voice)
Voice, VoIP and other related devices.
Cisco Stencils (Wireless)
WLANs, RF, etc.
Cisco Stencils (Security)
Firewalls, VPNs, etc.
Formal Network Symbols
This is an excellent stencil set of formal network symbols, for when the poofy internet cloud simply isn't enough. Oh wait — the poofy internet cloud is still there, hiding behind the moniker of "Network Cloud". That seems formal, maybe not black tie, but pretty formal.
Mac ADSL
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.