Reward is good: Blessed Prayer Beads (http://www.wowhead.com/?item=19990). There are not too many good healing trinkets in the game so make sure you got this quest.
(Thanks Front243 for the info)
Now you need to go to Felwood and bring 1 Felcloth (buy it at auction or farm it from satyrs in Felwood) to Impsy which is at 41,45.
Impsy will give you a follow up called The Wrong Stuff (both Alliance and Horde) where you need to collect:
-10 Rotting Wood
-4 Bloodvenom Essence
The Bloodvenom Essence drops of the Tainted Ooze next to Impsy (the green pool)
The Rotting Wood drops from Irontrees which you can find at 47,26 (all around there, look for big wanderers because they can drop more rotting woods at the same time.)
After you finished The Wrong Stuff go turn it in at Impsy
Now you well get the follow up called Trolls of a Feather which you need to do in Sunken Temple.
The feathers drop from the six guardians called: Zolo, Mijan, Hukku, Loro, Zul`Lor and Gasher.
After you completed Trolls of a Feather deliver it to Impsy and you can choosee out of 3 rewards:
-Soul Harvester
-Robes of Servitude
-Abyss Shard
-And 1 gold 55 silver
-And 6350 XP
In total for doing this quest chain which is not that hard you earn 3800xp + 5100xp + 6350xp = 15250xp and one of the most scythe looking staffs for warlocks (if you pick the soul harvester atleast).
(Thanks to Sulimo for this thorough piece of information)
http://wow.allakhazam.com/db/quest.html?wquest=8410 (obtainable from any trainer, for Alliance in SW and Exodar)
http://wow.allakhazam.com/db/quest.html?wquest=8411
http://wow.allakhazam.com/db/quest.html?wquest=8412
http://wow.allakhazam.com/db/quest.html?wquest=8413
(Thanks to Frsh for this thorough piece of information)