Without spoiling too much can anyone tell me if any of the Dark Brotherhood quests involved killing decent quest givers? I've just joined, but I haven't even done any of the initial contracts yet. Kind of worried about losing out on a cool quest here or there.

Nope, you won't kill off anyone too important (hee hee!).

Quest givers are usually marked Essential and are thus immortal.

Excellent, thanks for the info.

You could always save before the kill and reload if it says quest failed... but as far as I know you don't kill anyone of importance.

You do kill some "useful" people (Minor Dialogues or Merchants), but none Quest Giver (That I remember)

well you say that i have have aela the idiot die multiple times and shesone gives u wolf totemsshes so stupid glad i fnished last totem last night she gets lost every 5 seconds running off to fight things or not able to run up a bloody hill