Meazure - What are the dimensions of that image? How big is this window?
On-Screen Ruler - lightweight, free, semi-transparent ruler
PicPick - PicPick screen capture software enable you to grab an image on your computer screen, save, print, add effects, and share.
Measure Schmeasure - Measure Schmeasure is a simple screen ruler for measuring the width or height between pixels in any...
PixelStick - PixelStick is a tool for measuring distances and angles on the screen.
Meander - Measuring tool and route planning software for mac OSX