First, I'll start with FIRE by Kristen Cashore. I loved GRACELING and the world that Cashore had built, but I was so curious about this one. Ever since I read it, I still think of the main character, Fire, and how she's a monster with all sorts of complicated relationships to her family and loves. Also, I have fun imagining her hair. A lot. Read it, and you'll see what I'm talking about.
SHIP BREAKER by Paulo Bacigalupi (I had to practice saying his name so that when people asked me about my favorite reads, I could say it without sounding like a dork) is also a favorite. One of the things I adore about this book is how the world building is great, but it plays a flawless yet not-in-your-face second place to Nailer himself.
SERAPHINA, by Rachel Hartmann. This was a recent read. Though some of the spoilers aren't really spoilers at all, the crafting of this fantasy world is so well done. I felt Seraphina's uniqueness, and her mind garden (read it, you'll see!) was one of the most exquisite and beautifully done aspects of this book.
How about you? What are your favorite sci-fi and fantasy books?