Once you reach the mid to high 50's, there are many options open to you for grinding both levels and gold. Eastern Plaguelands is one of my favorite as there is one particular location that most people seem to overlook: Corin's Crossing.
At Corin's Crossing you will be killing loads of undead, so if you happen to be a Paladin, this is a great spot as your DPS will be much higher as well as your Experience per Hour. You will be grinding the following mobs:
The big draw for this location is not the mobs themselves but the chests that spawn in the buildings located here. There are four main spawn points for chests I have marked on the map below:
These chests spawn at about a rate of 6-8 per hour from my experience. It can be challenging to clear to them but if you are efficient, there is almost never anyone questing or farming here so they are all yours!
One of the mobs to watch out for here is the Unseen Servant which is invisible until it gets within aggro range. These seem to wander the area so be careful not to pull too many mobs at once because these seem to pop up at the worst times.