The 51-52 mobs at Sorrow Hill near Andorhal are the only things in WPL I bother AoEing anymore.. they last until 55-56. After that you can go to a few places.
As suggested, Winterspring can be good. There are 4 really good spots there. The first is the White Furblogs and the advantage of killing them is that you get Timbermaw Hold rep in the process. There's not alot of them though, and if you pick the wrong camp you get nasty casters. The camp near Everlook is a no-no, the one near the Timbermaw Hold exit is good.
The second spot is just over the mountain from Everlook. There are Owlbeasts, Bears, and Yetis there. If you go too far you'll get Chimeras that cast. Don't expect more than 3 mobs at a time though unless you get a great set-up.
The third spot is East of Everlook. There is a Yeti cave. At 56-58 I don't suggest going inside. Mount up and pull 4-5 of the Yetis outside at a time. None of them "cast" but Patriarchs have a Freezing Breath ability that is like a weak Cone of Cold. They still melee primarily.
The fourth spot is the best spot I know for 58-60 (cause the "cool kids" don't hit Outland till 60) but may be a trouble earlier. Southern Winterspring has a valley filled with caves and Owlbeasts of various kinds. It's easy to pull anywhere between 2 and 6 at a time there with a mount and there's enough that they start to respawn just as you're clearing it. The Moontouched Owlbeasts cast Moonfire so it's a good idea to keep their numbers down to 1 or 2 mixed in with the rest of your pull and kill them quick. Keep your hand on the Cleanse button.
And better yet.. There's quests involving killing all of these mobs as well yieling ~9.5k exp each, not to mention the skins that come out of it.
Edited, Feb 13th 2008 2:24am by Losie