Some vector tools have parameters like "arrowhead" that can be turned on and off, with different kinds, shapes and sizes of arrowheads. I know that Xara Photo & Graphic Designer 10 has that capability. I don't use Inkscape, because Xara does everything for me that Inkscape could do, plus a lot more. Even though Xara isn't free like Inkscape, you can download a fully working version for a 30 day trial I believe. I create all my professional maps using Xara, though I was sure that Inkscape had an arrow tool for lines.