Seeing as you are a Night Elf, might I suggest the Dirge of Teldrassil for Night Elf-centric RP?
(PM Vashava or Karinar for info!)
Otherwise there is the Ebon Onslaught for the true, neutral, Death Knight experience!
(PM Niallya or any other Alliance member for info!)
Ofcourse there is also Valormourne, who is currently trying to make a return to the RP-scene from what I heard!
Hope you find one of these guilds to your liking!