Visio alternatives that's not web based

reload@

So I just got a new job, and they don't have Visio on the laptop they gave me. I asked for Visio and they said it might be a while. I need to draw some network diagrams, but most applications I've seen are web based. I need to be able to draw diagrams even when I'm offline.

I assume the majority are using Visio, but I'm sure there are a few that have used other applications. What do you guys/girls recommend?