Imo, you can't beat yEd for diagramming.
One nice feature is that, in addition to the built in tabs full of icons, you can add your own & slowly build up a good library.
Here is a link to a bunch of free networking icons (2,173 of them !).
For Cisco icons, you can either learn German ;-) or load this page in Chrome & let Google translate it for you. It mentions that SVG version s of Cisco icons can be found at http://www.3dh.de/3dh.de/wp-content/uploads/2012/10/yEd_palette_CiscoNetworkIcons.zip and http://www.3dh.de/3dh.de/wp-content/uploads/2012/10/cisco_svg_icons.zip
Google around for
yED networking icons or
yEd Cisco icons and you will find more.
Have a look at the yEd gallery & see what you think.
Maybe not of interest to you, but yED can import from Excel and also text files in GML format. This would allow you to run a network discovery program to obtain information about your network, then code a simple program to covert that to GML and now you can auto-generate diagrams of a changing network, rather than having to edit your diagram by hand.