These are some Arduino projects that i found that may help SysAdmins.
I will add more projects here as I find them.

CDP Sniffing with Arduino

If your network switches support CDP, then this project will be able to tell you in which port you plugged this device. Useful if you have some majorly unlabeled network and you want to find out where a network port in plugged into.  

Arduino Network Relay Web Server

Control plugs remotely via a web server and a relay using Arduino.
Useful to reboot devices remotely. Especially ISP routers you don't have access to.