Well if you want something as dark and evil then I can point you to the clan Baali, from white wolf. These creatures seek to destroy and desimate everything with the use of demonic powers they obtain through the sacrifice of souls, ranging from fire, to shadow, to however the fury of hell becomes manifest to some physical form as bugs, disease, pestilence through the discipline of Daimoinon. (viable information can be found in all the white wolf books if you want to know what the truly hideous soul is capable of, and demonic investments/favor isn't something that is just religated to this fictional clan, or fiction in general, the story of Faust and Soloman are the real life versions of such.)
There are the Tzimisce, These are the old world, Romanian vampires from white wolf. They align to the Demon Azi-Duhaka who is an Offspring from the dark god Ahriman. And yes both of these demons and dark gods are real. Coven of the Darkest blood, has a section on them, or do a wiki search. But these guys manipulate the bone and flesh transforming themselves into what they will.
There are the Tremere who preformed a ritual when they imbibed the blood of some low gen Tzmisce, they transformed themselves into the same gen of the sacrifice they consumed, through diablarie made themselves a clan. However its these guys who perfected blood magick, and the control of the forces of nature through willing, shedding and focusing the power of the dark vite.
The Gangrel, are the ones who have an alignment to the earth, and transform themselves into the wolf, and mists, Where as the Tzmisce turn themselves into dragons through their disciplines.
The lasombara (Las Omri Bara - god of the river styx) these things transmute the shadows around them, as they are creatures who make use of the dark god ahriman, and use the power in their blood to manipulate the shadows, higher levels, they become a shadowy angel or demon depending on their mood.
The malkavians, are the crazy ones these are the type that at their highest level of power *shudders* can be in a town, get wind of something and cause thme to go insane by the combination of their disciplines and they don't even have to know anything about the person, just they exist, through their power they find them, can intrude their thoughts, and effect them with madness. There is a combination discipline using thaumaturgy (also a real path of magicks, part of the Heremtic teaching of miracle working, not be taken as theurgy or the working through the divine also what cermonial magic uses), when the malk stands on a hill, can focus on the target and squeeze their fingers and through the full use of their dementation power can cause the head of the target to explode. Its interesting to theorize as to how. But the rules for such things work.
There are assimites who are silient killers and their devolopment of their power of quietus can allow them any number of particualarly nasty effects.
The Nosferatu, are the diseased ones, spreading plauge and pestilences as well as being able to find out all the information and trading it to potential enemies.
Those are the fun ones anyway. There are more, but you have from the first version, to the third version with the dark ages series to get a firm foundation in these fantasy-classical vampires. Then there are the perversions of what is considered vampires in the requiem series.
