Tomorrow When the War Began! I love those books, although I'm a post-col/post-apocalypse junkie, and those hit all my kinks. They aren't in any way happy, but I found them immensely satisfying, for the most part, and the action sequences! Holy cow, they kept me on the edge of my seat, because like Joss Whedon, Marsden isn't too proud to kill people off.

These are good, and they're hugely popular in Australia. They're a bit dark, but I keep forgetting how many kids really like dark.