Earth Elementals at Stoneman's Notch are awesome for farming up Peridot Nuggets (5 power, 1% critical damage) and Piles of Radiant Dust.
Peridot Nugget | Pile of Radiant Dust
They have some decent abilities to defend themselves, so make sure that you are their level or higher when farming here. I used an XP boost and farmed for an hour, bringing in 80 Peridot Nuggets and 60 Piles of Radiant Dust. Although Pile of Radiant Dust isn't a super expensive item at the moment, I believe that they will become more valuable as more crafters reach the 150 skill level range. The Peridot Nuggets are great for my Enchantress at the moment, as I mix them in with gear that has a lot of precision and critical strike chance.
I haven't gotten to level 80 content yet, but perhaps there are earth elementals at the higher levels that drop really nice gems...