Quests for Razorfen Downs:
A Host of Evil
An Unholy Alliance
Scourge of the Downs
Bring the Light (Alliance Version)
Bring the End (Horde Version)

Razorfen Downs Level's 38-44 Located in The Barrens at the far south
There are 2 paths to go through in this dungeon. One leads to the Lich Amnennar the cold bringer and the other to Mordresh fire eye.

If you went after Amnennar then you will be fighting through alot of undead patrols. The dungeon is rather easy for a balanced group as each pull will have 1-3 elites and 2-5 normal mobs.
After a bit of killing you run into a abomination called Glutton he falls easily. Eventually you will get into a large room with a large spire in the middle. It takes a little while but you can pretty easily clear your way up the spire to Amnennar.

Amnennar is a easy fight just focus fire him down and his minions will dissapear. In my experience this dungeon has alot of nice caster loot.
Now Backtrack to the entrance and go down the other path. This side will also be pretty easy and is usually has pulls of 2-3 elites and maybe a couple normal adds. Eventually you will get to a room with a large gong in it. Clear the surrounding area the hit the gong. It will spawn spider monsters each time you hit it.

After around 3-4 hits it will spawn a large spider boss that has some nice loot but goes down pretty fast. Continue on till you find yourself in a large room with a huge bone pile. The bone pile has Mordresh at the top and he has 30 or so skeletal minions.
AoE the minions down and slay Mordresh and there ya go your done.