Emerald Lashers in Dragonblight can be gathered once they're killed and they drop the following:
Icethorn
Tiger Lily
Adder's Tongue
Lichbloom
The thing they drop the most is Crystallized Life Which sells for quite a bit on the Auction House.
It helps that the place they're located is a fairly popular quest hub and even during the day there are people in there killing the lashers so you can just run circuits around the area gathering all the dead bodies.
by klemmbob