It's a tie between:
The Monstrumologist by Richard Yancey
I don't want to spoil the book (in case you have yet to read it) but I found the plot very well thought through from start to finish. I'm not entirely positive who I would pick to play the main protagonist--William James Henry--because he's twelve years-old.
The Riddles of Epsilon by Christine Morton-Shaw
I loved the characters in this book, especially Epsilon (my favorite character). I loved the riddles he left behind for Jessica and how'd she solve them while learning past secrets. It really was remarkable to see her character grow.
As for the actors/actresses: Emma Watson as Jessica and Tom Felton as Epsilon. And yes, I know I'm picking two people from the Harry Potter movies, but what can I say? I think they'd be good for playing those characters.
Still Life with Crows by Douglas Preston and Lincoln Child (truthfully I'd like to see the series made into movies)
Now, I'm usually good at solving murder/mystery cases before reaching the end, but this book took an unexpected turn.
Agent Pendergast is one of the greatest puzzle/crime solvers ever to exist (besides the Riddler and Batman). The culprit took me by surprise and caught me off guard; I hadn't even expected that! It's an amazing novel--I had continued to read it even when I had gotten a cold and, although half of me wanted to sleep as one tends to when being sick, the other half refused because this book was too awesome to put down. More so when reaching (about) the halfway point.
It's hard to picture who best could represent Agent Pendergast; the guy is a unique character and it's hard to imagine an actor being able to stay in character. But if I did have to choose I'd pick: Cillian Murphy, Joseph Gordon-Levitt, or Garrett Hedlund. I'm sure I've thought of other actors over the past years that would make a good Pendergast but at the moment these three are the only ones to come to mind.