Omnigraffle (via the Omni Group)Omnigraffle is the best alternative to Visio for the Mac. In fact, it's one of the only ones I've found. It's very powerful and even has an iPad version. If you have to create network diagrams this is the app for you.
Selena has been at TechRepublic since 2002. She is currently a Senior Editor with a background in technical writing, editing, and research. She edits Data Center, Linux and Open Source, Apple in the Enterprise, The Enterprise Cloud, Web Designer, and IT Security blogs.