Dark Simulacrum, please go away. I don't think I even have you on my bars any more you useless POS skill.
Other than that for DKs, probably Pestilence - just bake it into Blood Boil like the T1 talent lets you.
And um, Control Undead, while kinda neat, I don't think I've ever used.
Besides that maybe some reworking of Icy Touch/Blood Strike/Outbreak. Not sure how exactly I would handle it, since it could become very imbalanced, very quickly if not properly done. I like the option to glyph Icy Touch as a purge, but I don't think I've ever actually used that functionality.
The only other thing would possibly be merging Frost Strike and Death Coil, or making Frost Strike also function as a ranged attack (though this might currently be offset by Howling Blast being one).