I'm surprised no one's mentioned Jellicoe Road by Melina Marchetta yet. This is one amazing book. It's about a 17-year-old girl named Taylor who's had some kind of difficult past, who tries to find her mother and make sense of her memories. And of course, the enigmatic Jonah shows up again, to add to it all. If you read this one, you have to keep going after page 100. It's a bit hard to follow up until that point, but it's totally worth it.
I think I'll re-read it; I've mentioned it, like, 4 times on this website :S
Also, try Saving Francesca. It's another amazing one by Marchetta.