I know that the Dark Brotherhood quests forces you to kill certain NPC's. So I am asking if anyone knows if the NPC's that you kill actually provide quests or services (like selling things, can marry, can follow, can train, etc).
For people that want to do all the quests, it would be important to know these details, as missing out on quests or services they provide would be a bummer.

Here are some from the followups:

Contract Kilings:
1) Kill Narfi: If you accept this mission from Nazir, you are not able to get mission: The Straw that Broke (finding Narfi's neckless)
2) Kill Anoriath: If you accept this mission, you are not able to get mission: Hired Muscle (beating him up for Companions quest). You are not able to purchase food from him later either (he is a merchant).

They might but the radiant story should fix it so that others become available.

Too bad it doesn't... at least not for Companion-related radiant quests.

Example: You can get a quest to "rough up" an NPC that you killed during a DB quest.

So the "rough up" quest gets cancelled if you did the Dark Brotherhood quest firsT?

No you get a quest to rough up a corpse. It's a bug in the Companion's quest though, it can also randomly select a character that was eaten by a dragon

I know of at least one:

Yes! we need to keep track of these things. For example, for some players we want to see all the quests, and finding a sequence to do certain quests later, in order to get access to more quests, is a good thing.
Who knows of anymore?

Found another one:

There's another with the house in Windhelm, doing that quest requires you to interact with a target for the Brotherhood. If I'm remembering correctly that is, I couldn't get the house on my first file because of that.

Do you remember any more details? I've updated the other ones people spoke of.

Found this:

"When the quest arrow sends you to Candlehearth Hall (when you are told to obtain a key to Hjerim from Tova), she may not be where the arrow says she is. No matter how long you wait, she will not appear where the quest arrow points to. However, this may have a correlation with the Dark Brotherhood quest "Mourning Never Comes", in which you kill Tova's daughter, Nilsine. Tova may be found dead, a note on her body explaining her suicide. She should have the key to Hjerim."

It's the blood on the ice quest. If you kill the shatter shield girl (optional target) during the dark brotherhood quest, the blood on the ice quest won't start. I'm not sure why, exactly.

I killed Nilsine before getting the Blood on the Ice Quest. I didn't have any marker problems, Tova was dead in her own house and that's where the marker showed she was. But I'm playing on the PC, and who knows what mysterious bugs have infested the consoles that aren't on the PC and vice versa....