Witch Doctor Mau'ari used to collect E'ko, and give various buffs in exchange for them. Since the Cataclysm, these rarely drop. They can't be turned in or vendored. They are auctionable for those with no scruples who want to sell worthless items to the unwitting, though. The buffs are now applied randomly when killing the relevant mobs. Obtaining one of each buff completes the E'ko Madness achievement.