Network discovery, what application are you using?

Many of us here work as consultants deployed onto customers networks to add equipment, solve an issue or advise on possible changes that could be made to improve the customers networks.

There is such a wide range of tools for network discovery these days, I have been using Advanced IP Scanner for a while that produces basic IP, hostname and service reports, and Nmap when I need a little more info.

But my question to /r/networking is.

You have been given permission onto a customers network, you sit down, plug in,

What is the first application you open to start your network discovery & reporting?

(And can it do SNMP info as well?)