Rui CarmoOmniGraffle is the closest thing to Visio on Mac OS X, and raises the bar in terms of what a drawing application should work like (its polished UI and helper guides remind me a bit of Aslhar Vellum, which I used many years ago):
Resources:
- Graffletopia, a stencil-sharing site that happens to have a great set of Cisco-oriented stencils.
Notes:
- Version 5 was released on Mar 6, 2008, with improved Visio support.