I am starting a couple of vampire hunting quests and I would really like a mod that improves the vanilla vampires. I would like something that makes them stronger or perhaps have more varied powers and attacks. If possible I want to improve their appearance to make them more interesting or more scary. Anything that adds new graphical effects would be great. I would be grateful if someone can suggest mods that alter some of these things. Many thanks for your comments.

There's http://www.gamesas.com/index.php?/topic/1082609-unholy-darkness-complete-vampire-overhaul/ by madmole, but that's still in development. If you don't want to wait, then http://tesnexus.com/downloads/file.php?id=16417 is good for making vampires much stronger, much easier on the eye, it will give them quite a few new accessories, and gives a very nice death animation.

Nature of the Beast.
Google it as
Oblivion mods nature of the beast

Thanks for the replies. I thought Nature of the Beast was mainly for player character vampires. I suppose it would alter NPC vampires in the same ways.

my favorite vamp mod for npcs is Duke Patrick's Nosferatu Class Vampires

I thought it added a big vampire fortress for you ( im not thinking of vile lair, i mean an actual fortress like fighters stronghold ) but i can't remember exactly.

I second that! Although I haven't played StarX's mod and compared.