Variety is the spice of life. At the moment I've got four books on the go (on top of an additional two that I'm not going to list that are being read for a couple of Bible studies):
Grid Resource Management: This one's kinda related to my thesis, but it's getting read in my "off" time as well.
A Tale of Two Cities: I can't remember the last time that I read a book in this category, bu it hasn't been a bad read. I'll blame the horror that was English class for my avoidance of this category of literature. After this book is done, I think that I'll begin The Brothers Karamazov