Network stencils
Free
Cisco Stencils (Machines)
Collection of hosts, clients and assorted support.
Free
Cisco Stencils (Wireless)
WLANs, RF, etc.
Free
Cisco Stencils (Voice)
Voice, VoIP and other related devices.
Free
Cisco Stencils (Security)
Firewalls, VPNs, etc.
Free
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.
Free
Network 3D
The following picture shows an OmniGraffle palette I put together for doing network diagrams. It may be useful for others.
Free
Cisco Stencils (Net management)
Various types of probes and management hosts.
Free
Cisco Stencils (Services)
Group of conceptual and functional icons.