KRuler

KRuler tells you precisely where your objects are in relation to each other

KRuler displays on screen a ruler measuring pixels. Position the 0 to your starting point (simple drag it), and read off (top left of the ruler) the precise pixel count to your cursor.

The context menu allows you to

Change the length of the ruler
Change the orientation of the ruler
Change the color and font of the ruler

In addition, under the pixel count KRuler will tell you the hex value of the color immediately under your cursor.