Elemental Goo

For lower level players, I suggest going to Mount Hyjal and killing the Scalding Rock Elementals right outside the door of the Nordrassil hub (the portal takes you here directly). Here you get the added benefit of assisting the guards or the guards assisting you. This would also be a great place for a level 85 to go, if you're in a hurry to get your quest done.

For mid 80s or level 85s looking to beat the crowds, you can kill some of the many elementals in Deepholm.

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• Right outside the Temple of Earth (the central quest hub) door and to the northwest there are Energized Elemental. They are levels 81 and 82 and are of neutral threat. These are also quest mobs and you may have a lot of competition for them. The northwest location is much less camped. The corpses can be mined.
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• East of the Temple of Earth is the Crimson Expanse subzone. It is FULL of Pulsing Geode and Fungal Behemoth which drop the quest item. These elementals are level 83. The Pulsing Geode corpses can be mined. Fungal Behemoths are the object of a Therazane daily quest, so you may wish to kill these if you are also doing dailies.
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This can also be found on elementals inside dungeons.

All five jewelcrafting dailies in Cataclysm have references to the TV show Futurama (some references have already been noted, simply cross-posting on all five quests):

A Present for Lila - Reference to the starship captain Leela, who also has purple hair. Also, reference to the robot Bender (Curver) and his constant drinking. (thanks for this to tonydizzle) EDIT: Upon completion, you also get a reference to the fact that Leela is a cyclops.

Elemental Goo - Reference to Professor Farnsworth and all the crazy contraptions he comes up with.

Nibbler! No! - Reference to spaceship captain Leela's pet, who eats anything and poops out starship fuel in the form of dark matter - hence, the "leavings" comment (thanks, Fortunate)

Ogrezonians in the Mood - Reference to episode 3x05, "Amazon Women in the Mood", in which the Planet Express starship crashes on the planet of the Amazonians (large females) who are ruled by the mighty Femputer. The penalty for the intrusion for all male members of the crew is "death by snoo snoo".

The Latest Fashion! - Another reference to Professor Farnsworth and his experiments and potentially to the show itself (stardust sounding like something from space, etc.)

As of patch 9.0.2, go to Deepholm and kill [npc=43123] in the red pools for [item=52506].