The idea of taking your current location and emailing it to one of your contacts is super simple, but super effective. If the recipient opens the resulting URL on their iPhone, it'll pop open the GMaps app and show exactly where you are, which can then be used as an endpoint for driving directions.
We just tested it ourselves and got to within 24m accuracy, which is pretty darn good for sitting on a couch inside a house. It's free, and you should download it now. Don't be confused with the other app named Here I am, which is much lousier. This one has an envelope icon. Grab that one here.
Stupid note: When you send an email, the subject reads "hereIam", which looks a lot like "HereLam" when read on the iPhone. Seeing as I was testing it out by sending my location to Lam, it was kind of funny. Thus ends the most boring anecdote you will read today.