Meazure - What are the dimensions of that image? How big is this window?
Magnifixer - Magnifixer is a screen magnifier utility.
On-Screen Ruler - lightweight, free, semi-transparent ruler
gpick - A color picker and color scheme creation tool.
Measure Schmeasure - Measure Schmeasure is a simple screen ruler for measuring the width or height between pixels in any...
gcolor2 - GTK+2 Color Selector