I used Omnigraffle about a year ago then I remember I had difficulties to draw network diagram based on Cisco Stencil. I posted Cisco Stencils for Omnigraffle and that was pretty much the only available Cisco Stencil during that time.
I’m reopening my Omnigraffle ’cause I’m quite lazy to switch to other laptop and start googling for Omnigraffle stencils. I’m quite surprised to know that there is actually a site dedicated just only to provide free Omnigraffle stencils and it includes Cisco stencils. Graffletopia gives you heaps of Omnigraffle stencils for free. The quality is very good and although not all of Cisco stencil are available, it is actually enough to start the work.
Big thanks to Patrick Crowley for the initiative!