I came up with areas for the element bosses while I was supposed to do something important.
1. Water: Dragonblight/The Crystal Vice - Winterspring - Azshara. Azshara was a naga queen.
2. Fire: Un'Goro Crater/Fire Plume Ridge - Searing Gorge - Burning Steppes.
3. Earth: Thousand Needles - Blasted Lands - Desolace.
4. Air (I prefer it to be called Wind, though): Silithus and I cant figure of anything windy or "airy" other than that.