The Demonata Series, by Darren Shan (Cirque Du Freak, among others) is one of those great series.
It is a ten book series focusing mainly on three characters that, for better or for worse (excuse the cliche), are the saviors of humanity.
Now, I'm not going to spoil the books because that would be rude.
If you are looking for epic battles, intense relationships and morally grey-subject matter, then this series is for you!
The Demonata Series, by Darren Shan!
First book is "Lord Loss."