Skulduggery Pleasant

Several of my friends have called this "hands down the best YA series ever written". Personally, I don't think I'd go that far, but I must admit its one of the better ones out there. The characters are well-written, the story is gripping, and Derek Landy's writing continues to be extraordinary.

This is probably the only YA novel I've read where romance is handled in a completely reasonable fashion -- upon the protagonist's realization that their significant other is a flesh-eating vampire in a universe where vampires don't have the chance for redemption, their response is not to pine after them endlessly for several chapters trying to make it work despite the inevitable fallout. The author gets a huge amount of bonus points for that.