A year or so ago, my friend introduced me to Vampire Knight, and I used to read it online, but, when I found out it was out in book form, I bought 2 volumes of it. And of course, I still enjoyed every moment of it.
The basic setting is a boarding school (Cross Academy) attended by both humans and vampires (who, by the way, are not the undead, just a seperate species from us - also, their existence is a secret in this universe, like it is in most vampire novels). Vampires attend the Night Class, and humans attend the Day Class.
The Chairman of the academy, Kaien Cross, adopted a young girl called Yuuki 10 years ago, when she was left out in the freezing snow, and attacked by a crazed vampire - however, she was saved in the nick of time by another vampire, Kaname (Kah-nah-may) Kuran, and brought to the Academy. Kaien also adopted a boy called Zero 4 years ago, whose entire family were killed by a vampire. Yuuki and Zero are prefects, who keep the vampires' secret from the rest of the students (they just think that the Night Class are geniuses, something along those lines).
Now, Vampire Knight has a few interesting differences in its vampires. There's a pyramid in Vampire Knight for ranking a vampire's nobility. Level A means there's no human blood in their family at all, and they have lots of special powers (they're obeyed completely by other vampires), Level B are aristocratic vampires with special powers, Level C are common vamps, Level Ds are ex-humans, and Level Es are ex-humans who can no longer control themselves. Kaname is a Level A, so he's highly respected by the Night Class in Vampire Knight. Also, the new technology in this universe has made 'blood tablets' that you just mix with water - a substitute for blood.
A synopsis of this book - Yuuki and Zero are protecting the vampires' secret from the Day Class, however, lots of flashbacks and lone contemplation from Zero show that he's got a secret to hide too...
So, in a nutshell, it's a very interesting story, and, if you've finished other vampires books and are looking for something different, this is right up your street.