CADE (free)Cade is a tool developed by a company that focuses primarily on CAD. CADE is a 2D vector editor for Windows that can handle the task of diagramming your network with ease. One feature I really like about this tool is the ability to notate IP address, serial number, and manufacturer for each piece of equipment. CADE has all the stencils you need for a complete network diagram. CADE is free to use.
See the blog post, "Diagram your network with these tools", for details on submitting your own network diagrams.