I really don't read much fiction at all... I used to read more fiction in high school and liked John Donne a lot.
Damn, looking at my book case, I don't read any fiction at all. Most of my non-fiction comes in the form of video-games. So...I don't really have an anything of all time, but the books I enjoyed most most recently were, in no particular order.
White Like Me
The Elegant Universe
Nerds: Who They Are and Why We Need More of Them
Mexican American Girls and Gang Violence: Beyond Risk
Defending Humanity: When Force Is Justified and Why
Being all the rave while I was in the Army, I do have On Combat and On Killing and wanted to finish both of them but people always want to borrow those (I think I was about halfway done with both of them...I may have finished On Killing, actually...and remember it being pretty decent).
Yeah, I tend to read more about things having to deal with quantum mechanics, sociology (also read a ton on porn and pornstars. Pornstars, the actual people and their lives outside of porn- before, during, and after it- are one of my biggest areas of interest), and psychology. Not against fiction of anything, but I really have to like the characters AND the plot to be into a fictional book (probably also the reason I have so many RPG and action games that I've yet to complete).
I haven't had much time to read because of school, but I did buy 400+ dollars worth of books earlier this year.
Oh yeah! I wanna read the Parasite Eve book, even though it sounds silly! I'd probably like the Dragon Age and Mass Effect books, had my Warden/Hawke and Shepherd been the protagonists, too. =(
Oh yeah, one book I recommend to ANYONE is Thomas Hobbes Leviathan. I used to be much more into philosophy until I took it in college.
Okay! Last edit! But I can't mention Leviathan without mentioning Sun Tzu Art of War and Mao's On Guerilla Warfare for some reason! Possibly because I was in Afghanistan when I read it, but I appreciate Mao's book much, much more.