Every Day by David Levithan is one of the most original teen books I have ever read. It is the story of someone named A who wakes up in a different body every day. A only gets one day in that person, boy or girl, it doesn't matter. A knows no other life; he/she has always lived this way. It is difficult to connect to anyone when you are shifting lives all the time, so A is truly surprised when he/she meets Rhiannon while spending a day as her boyfriend Justin. It could be love, but the only way to know is to try to return to Rhiannon (as other people) whenever possible.
Every Day is told from A's perspective; Another Day is the same events from Rhiannon's perspective. Fortunately for me, it has been a long time since I read the first book. I had forgotten enough of the story that this was one was fresh and new to me. The stories are so parallel that you could probably alternate back and forth between them to get the full perspective.
In the first book, we learn about each person that A is inhabiting and the daily struggles of learning all about their lives. We also see A struggle to return to Rhiannon without disrupting the life he/she is inhabiting. In this book, we follow Rhiannon as she struggles with the idea of someone like A existing and how they could ever be together.
I think I would have enjoyed this book less had I just read the first book. Still, I recommend them both. It is a fascinating story about sexual identity and judging people based on their outward appearance.
For more info, check out the Indianapolis Public Library catalog and the author's site.