Graph paper and pencil.

A good KD won't need it, and a bad one won't tell you what's wrong with it. Don't propose anything to a cabinet company without vetting it here first. 80% of Lowes cabinet salespeople can't tell a good design from a bad and don't have a clue about what building codes you may be violating. You need the extra eyes that this forum can provide.

A good tape measure to give you perfect measurements on your graph paper and a good ruler to draw nice straight lines with your pencil.

I do love graph paper.... but the ability to see it in 3d is so tempting!

Doubt it's the best, but since you want it to submit to Lowe's, might as well use Lowe's.

http://www.lowes.com/cd_virtual+room+designer_189310537_

Spent some time with the graph paper this afternoon -- very helpful. Did both a floorplan, as well as elevation drawings of each of the walls.