Any carpenters or architects reading this? Leave your measuring tape at home and download the Advanced Ruler Pro app on your Android phone, which measures the height of buildings, people—basically, whatever you aim it at.
You'll have to enter your own height into the app first, deducting a couple of inches if you hold the phone at eye-level or chest-level. That way the app will know roughly how high off the ground it's being held, so can get on with measuring an estimate of the object in front of you.
It supports both imperial and metric measurements, first measuring the distance between yourself and the object, and then the distance between the bottom and top of the object. 99 cents isn't bad for what could potentially help you out in situations involving getting cats out of trees, or buying a new ladder for fixing that broken gutter. [Recombu]