Sometimes, the skills were worthless, and it's a good thing they went away (or at least, not a bad thing). Sometimes, though, we really did lose something special. For me, the talent that always makes me a little verklempt is Unholy Blight. Back in the early days of Wrath, Unholy Blight was an engine of destruction. For around half your runic power bar, it would summon a swarm of insects that would surround you, inflicting AOE damage to all enemies in melee range of you and infecting them with a disease that would make your strikes hit harder.
This, of course, was incredibly powerful. It made keeping threat as an unholy tank a breeze, and it made sure unholy DPS death knights topped the damage charts whenever there was an AOE fight. But what really made it awesome for me was the way it made me feel. I was a death knight, a walking tower of death, decay, and fear. My aura of malevolent power was so amazing that my enemies felt it gnawing at their very souls. That's why, whenever I look at the current talent and its silly little Death Coil damage boost, a single tear rolls down my cold, undead cheek.
What about you? Whether they've been removed or just nerfed beyond recognition, what old-school spells, talents, or skills do you miss?