I use a triangle ruler =) This makes panelling very convenient because you work parallel to the page borders due to the markings.
My measurements are 2cm from the bottom and 1,5 cm from the other page borders. As you can see I just have to place the ruler where I want and voilà =)
From a How-to-draw-manga-manga by Akira Toriyama I learned that the horizontal spaces have to be bigger than the vertical ones. So for horizontal ones I take the bottom of the numbers printed on the triangle ruler (sould be ~8mm), for the vertical ones I use the end of the mm markings (~3mm)
And the result looks like this: