I'm not sure if anyone has read this series before, but it's really good. Here i basically what it is about. ( from wikipedia )
Night World is a series of nine young-adult fiction novels written by L. J. Smith. The series takes place in a world similar to our own but one where vampires, witches, werewolves and shape-shifters live among humans without their knowledge. These supernatural races make up a secret society known as the Night World, which enforces two fundamental laws to prevent discovery: 1) Never allow humans to gain knowledge of the Night World's existence and, 2) Never fall in love with one of them.
Each volume of the series follows a different protagonist (always a teenage girl) who must face various challenges involving love, the "soulmate principle" and the Night World's strict code. In the first six novels, the plot focuses on the protagonist discovering her soulmate and the danger which ensues. In the seventh book of the series, the concept of an impending millennial apocalypse is introduced. Although the theme of the "soulmate principle" continues to be present, the plot now focuses on the search for four "Wild Powers" who, according to an ancient prophecy, will either save the world or aid in its destruction. The series has been on the New York Times Bestseller List for children's books for 22 weeks as of May 19, 2009.
The concluding book in the series, Strange Fate, has been delayed for a decade and is now scheduled for release in winter of 2010.
There are three volumes out right now. Three books are in each volume. I hope you read it! It's so awesome! MY fave character is Ash. You will know who that is if you have read the series.