We all know this scenario:
You're sitting near the bank waiting for the guy to show up whose service you picked up through the trade channel and you can't find the guy because the bank is covered in mammoth riding level 80s that have nothing better to do than sit there and block your view.
Sure you will eventually find each other, but the longer it takes the more frustrated both of you will be and the less pleasant your interaction may become.
Thankfully jewelcrafting comes to the rescue and these days you will often find these sitting on the auction house for a nominal fee (just search lens on the AH):
What this puppy does is project a pretty beam of light much like the warlock's drain spells on the target. The range seems to be pretty high and the target can even walk out of LOS without losing the beam.
Not only does this little lens come in different colors and make an incredible tool to find people you can also use it to point out different objectives in instances or point out targets for those that have their video setting set lower and don't see everything. It can also help to mark objectives in BG's and there's about a dozen other fun things you can do with it. Incidentally it's absolutely bloody brilliant to find named mobs with that are always hiding in some obscure little corner.
With jewelcrafting 350 and only requiring a green quality gem to make this 40 charge lens I happily recommend it to anyone who has to deal with finding people or pointing out things on a regular basis.
Not only that but if you give it to 25 others you can make one hell of a lightshow.
Give it a try if you haven't yet.