This plugin provides some basic functionality that I was unable to find with any other plugin.
On checkout, if the user has entered a state in the Continental United States (Lower 48), the only shipping option available is “Free Shipping”.
If the user enters a state that is in the United States, but not in the lower 48, it shows the flat rate.
I created this plugin for use in some of my WooCommerce installations, so it is not editable in the panel. I figured that someone else might find this usefull, so I am throwing it here. If there is a lot of support behind this plugin, I may think about adding some more customizability to it.
Verified working in WooCommerce 2.3.8