Stuff more like Damnation?

As someone else said, Katatonia is good. Especially Last Fair Deal Gone Down. Porcupine Tree is also a good choice, especially Deadwing or In Abstentia (Darker than Damnation and not all mellow. But all clean vocals).
 
The only DT song which I can say that it sounds similar to Damnation is "Repentance". It even has Mikael and SW on it.