Google Earth is a great resource for engaging students in learning by using real world places and great visuals. This is the first in a series of tutorial videos in using Google Earth in the classroom.
The ruler tool allows teachers/students to measure distances of real world objects without leaving their classroom. You can measure the distance around an object, between point A to Point B or find diameter and radius.
You could also use this in Social Studies when discussing where things happened and how far things are from each other. What did it mean to cross the Atlantic Ocean as a pilgrim? How far did Santa Anna travel from Mexico City to San Jacinto?