I recently read The Twilight Watch, the 3rd book in a fantasy/ sci-fi series (Night Watch and Day Watch are the first two books) by Sergei Lukyanenko. Movies have been made of some of the stories from the first two books, but they are nowhere near as good as the books.
Each book is divided into three stories. The stories are set in a universe filled with magicians, vampires, werewolves, and other supernatural beings. There are basically two kinds of beings - magical and non-magical. Within the realm of the magical beings, there are two sides - the Light and the Dark. These sides have made an uneasy pact to not obliterate each other, but to keep the Balance. Enter the two Watches: Night Watch and Day Watch which 'watch' each other, or keep each other from upsetting the Balance.
These books are definite page turners, the kind of books that I am compelled to read it - they call out to me, 'read me, you know you want to...' They are so amazingly good and are three of the best books of any genre that I've ever read. So put these on your summer reading list if you're into fantasy & sci-fi.