How do I get the IP external to my local network given by ISP?

So you have a local network on the 192.168.*.* subnet. My router is somewhere on 192.168.1.1 or 192.168.1.254. Now what am I known as on the internet? What is my IP for the internet, ie what is the dynamic IP that my ISP has given me? HERE IS THE ANSWER, once you have this you could script things ....

Where Did My Office Computer Go? Scan IP ranges for a service

So I lost my computer, since the network MAC->IP cache was flushed, however I know the subnet and the machine is on. But its a headless piece, no monitor. Where oh, where did my computer go??!?!?! Wireshark is more for recording what comes in, other network utils are on a IP basis... but lets curl ourselves out of here... I want to validate the existence of a twiki site:

curl -f -m 2 http://10.10.10.[100-200]/twiki/bin/view

Yeah its that easy.... and easy to forget...