Daystar is good but the best weapon against vamps is definatly the upgraded mace of disruption it can be found.....
Spoiler
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In the graveyard, in the vampires lair to be precise.
Take it to cromwell the dwarf in the docks district along with the Illitium from the sir Sarles quest (temple of Helm, temple district) and he will make you a mace wich grands immunitie to level drain and kills undead in a single blow.
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Those who watch their backs meet death from the front- Dreamer128 paladin of the order of the holy flame.