Here are some Australian titles to add to the American dominated list of teen books you've compiled. These ones mostly appeal to girls since they deal with the life and tribulations of teenage girls (mainly in high school
Feeling Sorry for Celia - Jaclyn Moriarty
Finding Cassie Crazy (US title:
The Year of Secret Assignments...I think) - Jaclyn Moriarty
These two books are wonderfully funny, light reads that are composed entirely of letters written by and delivered to the protagonist/s of the stories. Some of the letters are from real people (like the students of neighboring schools who are participating in a letter exchange system instigated by their English teachers that was meant to re-introduce the "joy of the envelope" and "forge school ties," but instead resulted in most of the students telling the teachers to stick it up their respective arses.) Some letters are from imagined organisations like The Society of People who are Definitely Going to Fail High School (and Most Probably Life as Well!) Very fun reads.
Looking for Alibrandi - Melina Marchetta
Saving Francesca - Melina Marchetta
Melina Marchetta write enormously popular teen books over here in Australia, despite the fact that she's only written two so far. Her female characters are always gutsy and opinionated, although some don't necessarily present that facet of their personality to the rest of the world all the time. Marchetta's particularly strong at writing believeable and amusing friendship and familial interaction, drawing on her own experience with her extensive Italian family and her observations from being a high school teacher. Upon these relationships, she builds the story of a year in the lives of her two main protagonists, Josie from "Looking for Alibrandi," and Francesca from "Saving Francesca," covering events like suicide, depression, family breakdowns, miscarriage, Colin Firth as Mr Darcy nights, 15 girls attending what used to be an all boys school etc. I recommend them so much, but Saving Francesca may be an easier one to start with because it was written more recently, and thus the pop culture references in it (of which there are many) are still fresh and relatable.
Queen Kat Carmel and St. Jude (get a life) - Maureen McCarthy
Chain of Hearts - Maureen McCarthy
McCarthy's books are probably the hardest from my list of recommendations to get a hold of in America, but they are just so great that I feel it's well worth any effort. "Queen Kat...etcetc" is about three girls in their first year of uni who share a house in the inner city suburbs of Melbourne. Each girl narrates a third of the book and their individual voices carry a rich and varied personality that is reflected in the myriad of occurences and obstacles that beset them: drugs, death, self doubt, eating problems, and probably worst of all, love.
"Chain of Hearts" is about a girl who has become bloated, depressed and resentful after the death of her best friend in a car accident. After much prompting by her perfect WASPish mother, she agrees to stay with her artistic aunt in a rural Australian town. There she learns about her family history and secrets and in the process rehabilitates herself. It doesn't sound like much - none of these plot lines do really - but it's all in the character creation. This books spans a time period from the 70s when the protagonist's mother and aunt were in
their teens to the end of the main character's prolonged stay at the town.
Sorry for the length. I'd also recommend Francesca Lia Block for those who enjoy heavy imagery in their prose.
I realized that. 
so boring 
the beginning ones were much better.
