QuestHelper displays a directional arrow.. you might dig into the code there and see if you can re-tool it a bit for your purposes. Offhand, it seems like that with some of the mini-map ping code in the forums here could maybe get you pointed in the right direction (so to speak...)

edit::
just checked out questhelper over on Curse and noticed this:
How do get that 3D arrow pointing where to go?

That arrow is part of Cartographer Waypoints. It should appear automatically as long as Cartographer is installed and running, and you haven't turned off that feature.
So, check out Waypoints too!