Endless Hunger
Sometimes you just get the urge to kill someone, and sometimes, you have to kill someone in order to complete the quest Endless Hunger.
Runeforging: Preparation for Battle
You've got some new snazzy weapons to stab people with, so now you'll need to forge some runes on them in Runeforging: Preparation for Battle.
The Emblazoned Runeblade
You've made yourself a new Death Knight, but you kind of need a weapon to go with your looks, right? The Emblazoned Runeblade helps you with Runeforging.
In Service of the Lich King
In Service of the Lich King is a simplistic walk to another quest giver quest, but it also signifies the start to your Death Knight days.