This is purely for lvl 70's:
#1) Pass the gate into shadow labs, inside it mobs are coming out of the instance portal and fighting the guards, if you attack them they will almost _NEVER_ aggro you, so you can just peacefully level up your weapon skill!
#2) Come out of the dark portal leading to outlands, there's an elite and he just won't die (he stops losing health as soon as he reaches 1%)
--> I've personally never tried #2, I just noticed it while i was riding around and thought that it would have been a nice place to level up weapon skill ! But really just stick to #1 it's an awesome place to level it up if you don't like running around slaying rats in ironforge (aah the good old days when I was a noob + alliance )
-Draz