Isoscope shows you how far you can travel from any location in a given amount of time. Could be really useful when you consider the next item:
NUKEMAP is for the more paranoid of you. It lets you detonate a hypothetical nuclear weapon and see what the damage would be like.
A map of all the tornado paths in the US since 1950. Tornadoes don’t seem to like West Virginia.
Regular expressions are super useful. RegExr will teach you how to use them.