The Lunar Chronicles by Marissa Meyer
I was not expecting to love this series as much as I do. I'm not completely caught up (I'm about half way through Cress) and I know the series isn't even completed yet, but I know it's going to be a favorite. I love how fairy tales are used as inspiration, but that the story and characters are so much more than those fairy tales. The idea of cyborgs and a war with the Lunars (those who live on the moon) is just amazing. Not to mention I love how Meyer writes female characters, their each their own person and totally kick-ass! (Also, best covers ever!)
Across the Universe by Beth Revis
I fall more in love with this trilogy each time I read it. I adore the main characters, Amy and Elder, and how the story is told from both their points of view. This was my first experience with sci-fi in the young adult genre and I was totally blown away with Revis' killer story telling. It's been years since I originally read the first book and I still remember not being able to put it down and then going to the bookstore the day A Million Suns came out because I just had to know what happened! Each book was seriously incredible on its own, but when the three come together to form this kick-ass story it just becomes other worldly.
Shatter Me by Tahereh Mafi
What I love most about Tahereh Mafi's Shatter Me books is the writing style. I love how you can see Juliette growing and changing throughout the story through her voice. I also adore how you original opinions are challenged and how Mafi twists the world to make you look again.
Delirium by Lauren Oliver
Delirium was one of the first books I fell in love with. The whole concept of a world without love drew me in and Oliver's amazing writing and characters kept me reading throughout the trilogy. Even though I know a lot of people weren't a fan of the ending, I adore it. It still makes me think even though it's been a long time since reading it.