All in the title.

The main piece of evidence toward Vampires still being "alive", I believe, is the fact that Vamperism is a disease. How could a disease survive in Undead tissue? Much less the fact that Vamperism progresses in stages, and can affect a large-scale mutation in the case of a Vampire Lord.

Now I know what you're about to post - Detect Dead. It works on Vampires, and can even be used to detect those in the first stage of the disease. However, is the spell really the best indication that Vampires are infact undead? It's more then possible that the spell isn't sensitive enough to tell the difference between a dead automation and a Vampire due to the massive slowdown of the infectee's metabolic processes, which results in the effective immortality Vampires possess.

Well, apart from other multiple spells that affect only the undead (Turn Undead variants) and spells that CANNOT work on the undead (most healing spells)

There's also:

The disease takes hold of living tissue. When vampirism goes into effect, it ceases to be a disease. And yes, they are undead. It's been confirmed many times about them. My main question is whether or not they could be considered daedra.

I have wondered about vampires being daedra as well i remember someone on this forum saying daedra don't like vampires and for obvious reasons.

Not sure if its all Daedra don't like them (well clearly Molag Bal favors them) but that point is raised by Count Hassildor of Skingrad during the Oblivion Crisis. He specifically says something to the lines of "Mehrunes Dagon and his ilk have no more love for my mind then yours. Perhaps less, as we make poor servants."

Somewhere I had read that vampires are technically dead but at the same time living just with their soul...misplaced or tainted, I don't remember the exact term for it.

You can detect vamps with detect undead thing so they must be considered dead to some point.

Vampires, are indeed, dead. Or rather, Undead. In TES II: Daggerfall, 72 hours after your character contracts Vampirism and fails to cure it, you actually die, and awaken in the nearest crypt. Because you died, you lose all of your ranks within any guild you were in, which was a serious problem if you were in a guild that would invite you only once, like the Dark Brotherhood or Thieve's Guild.

This.

For some reason Bethesda has just made you "transform" into a vampire instead of actually dying. No idea if it's a good thing or not though, but I'm sure some people are annoyed about it. The only real thing that would upset me is if you did lose all ranks (which is now just membership) with whatever guild you were in, but I'm sure that would never happen again.

Also, for once the ritual to cure it actually suggests you are dead - it involves a black soul gem, maybe they're literally replacing your soul to bring you back to mortal life.

Wouldn't we also have to consider werewolves daedra as they gained their power from a daedric prince?

When I did it he offered the soul to the gods in exchange for returning yours

Ahh, I've never actually done it I just knew about the soulgem. So basically as a vampire you're soulless... wait, can you soultrap other vampires?

Yeah actually I'm not sure what he exactly says but he offers the soul to the gods maybe it is just for life not for a soul

I think vampires are half daedra cause molag bal used his blood to turn lamae beogflag and most likely bal turns people into a pureblood vampire via his blood.

There are too many confirmation that vampires are undead in the ES. I can quote about every book that says they are undead or speaks of their death. But when they are given the disease, they wait for three days. On the third day, the infected dies and becomes a vampire.

Same for Serana, I suppose. Lamae was turned into a pureblooded vampire, but she still died after Molag ravaged her. After he dropped his blood on her forehead and she was taken by the Nedics, she passed onto death and was reborn as a vampire. A walking corpse.

Somehow, marrying her becomes much less appealing when you describe her like that.

A beautiful walking corpse that does not rot . Better?

As far as I understood it they exist between life and death, hence the undead thing

You are correct.

As a side note, do the Sunfire, Stendarr's Aura and Vampire's Bane spells disintegrate the undead?

Not that I know off. Never happened to me.

I was wondering why if I'm a dead vampire, I start to drown if under the water to long?

yeah, that annoyed me as bit to. the dead shouldnt need to breath lol

It is strange. Vampires can sweat, they can breathe(Serana makes a comment about breathing the fresh air).

No. It makes the prospect even more sixy...