Poisoned Water (56)
Starts At: Duke Hydraxis - Azshara
Zones: Azshara, Eastern Plaguelands
Use the Aspect of Neptulos on poisoned elementals of Eastern Plaguelands, which transforms them into the mobs you need to kill. Collect 12 Discordant Bracers and bring them and the Aspect of Neptulos to Duke Hydraxis in Azshara. The elementals can be found in a few pools in the Eastern Plaguelands; the small pool to the south of the zone is the easiest one to complete the quest.
Stormers and Rumblers (57)
Starts At: Duke Hydraxis - Azshara
Zones: Azshara, Silithus
Travel to Silithus, kill 15 Dust Stormers and 15 Desert Rumblers, and return to Duke Hydraxis. Both mobs are most easily found in the Crystal Vale, in the northwest part of Silithus.
Eye of the Emberseer (60+ raid)
Starts At: Duke Hydraxis - Azshara
Category: Upper Blackrock Spire
Kill Pyroguard Emberseer in the early stages of Upper Blackrock Spire and bring the Eye of the Emberseer to Duke Hydraxis in Azshara. The Emberseer is in one of the first rooms of UBRS, and is a trivial kill for most raids.
The Molten Core (60+ raid)
Starts At: Duke Hydraxis - Azshara
Category: Molten Core
Kill 1 Firelord, 1 Molten Giant, 1 Ancient Core Hound and 1 Lava Surger, then return to Duke Hydraxis in Azshara. These mobs are all run into fairly early on in Molten Core, before reaching the first boss.
Agent of Hydraxis (60+ raid)
Starts At: Duke Hydraxis - Azshara
Zones: Molten Core
Earn an Honored faction with the Hydraxian Waterlords. When you're halfway through Friendly, you can only gain faction by killing the Emberseer in Blackrock Spire, and by killing mobs and bosses in Molten Core -- a few runs through MC should get you Honored.
Hands of the Enemy (60+ raid)
Starts At: Duke Hydraxis - Azshara
Category: Molten Core
Now things get tough: Bring the Hands of Lucifron, Gehennas, Shazzrah and Sulfuron to Duke Hydraxis in Azshara. If your guild can kill all these bosses, you're just about ready for Ragnaros.
A Hero's Reward
Starts At: Duke Hydraxis - Azshara
Zones: Azshara
For defeating these bosses, collect your reward from Hydraxis' Coffer, under the surf at the southern base of Duke Hidraxis' island. You can choose from two rings: Ocean's Breeze or Tidal Loop, both with +15 fire resistance, which will come in handy when you finally face off against Ragnaros.