I looked through quickly and never saw this posted (Im tired as hell and just found out, so if it's been posted already just delete this). It wont even get you banned because it's not exploiting the game
If you got a buddy that's a high lvl druid get him to go moonkin and spec in Brambles 3/3. Have him cast it on you and just run out and aggro every mob you can by smackin them. As long as you hit it once before the the damage shield does you'll end up 1 shotting the mob and getting the sweet sweet XP.
I levelled from 1-17 in a few hours doing this on my little druid with the lvl 80 duel boxed on auto follow. It does around 125ish a pop, and this was a druid with little casting gear on with brambles 3/3.