The in-game information in this article is kept purely for historical purposes and may not need to remain under any other categories.
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.
E'ko buffs and mob sources
Info from "Ek'o Madness" comments at Wowhead.
[Juju Frenzy] - from any Winterfall Furbolg in Winterspring (68,50 East of Everlook).
[Juju Mending] - from Shard Tooth Maulers (Brown Bear) (59,40 around Moon Horror Den).
[Juju Fury] - from Shy-Rotam (Frostsaber Cat) (47,19 Frostsaber Cave).
[Juju Chill] - from Icewhomp (Yeti's) inside the Cave (67,54 South East of Everlook).