Uglies - Scott Westerfeld

Tally can't wait to turn sixteen and become Pretty. Sixteen is the magic number that brings a transformation from a repellent Ugly into a stunningly attractive Pretty, and catapults you into a high-tech paradise where your only job is to have a really great time. In just a few weeks, Tally will be there.
But Tally's new friend, Shay, isn't sure she wants to be Pretty. She'd rather risk life on the outside. When Shay runs away, Tally learns about a whole new side of the Pretty world - and it isn't very pretty. The authorities offer Tally the worse choice she can imagine: find her friend and turn her in, or never turn Pretty at all. The choice Tally makes changes her world forever.