Three books which have 'explained' where we are with physics have blown my mind. Each one was mindblowing in its own way, but the effect was less with each book due to already knowing the subject matter a little:
Bill Bryson - A Short History of Nearly Everything.
This obviously only skims the surface with the details, but it's deep enough to give you some clue as to what is going on, and it's aimed at the non-scientist, and his way of explaining things is very easy to understand. Being interested more in physics after reading this lead me onto:
Brian Greene - The Fabric of the Cosmos.
Much more details than Bill Bryson, and I believe his metaphors were better, giving me a greater understanding of the ideas. Had me gripped until the last few chapters which were about String Theory and M-Theory, which I'm not a fan of at all. Sounds like total bollocks to me, but who am I to disagree with the world's best scientists?
Steven Hawking - A Brief History of Time.
I only read this because it's such a famous book and I wondered if it contained anything that the others didn't. A lot dryer than the two previous books I've mentioned, and obviously a lot older, so some things were missing. Again, the latter sections on black holes seemed 'wrong' to me, but I realise Hawking was one of the pioneers in this field, and so I'm not sure how far his theory was developed by then. The worst of the three books for readability, but probably the most important in terms of getting information out to the general public when the time it was written is taken into account.
If I was somehow able to read them for the first time, I'd have read Hawking before Greene.
As for fiction, the most mind-blowing book I've read...Hmmm, I'd say it's a toss up between Catch-22 and 1984. Not very original, I know, but there's a reason these two are rated as highly as they are!
1984 - First book I'd read that wasn't trashy, pulp stuff, and got me turned on to more interesting things. I've often said it's my favourite book, but I've never read a book twice (yet) so I'd like to go back and re-read it to see how it compares to my more 'explosed' mind. I'm sure it'll stand up fine though.
Catch-22 - Started this twice and stop reading because I couldn't make sense of it. I think I just wasn't in the mood. One day I picked it up and started reading, and I realised for the first time it wasn't a serious book! I knew nothing about the book apart from it was a war story and it was a classic. It all made sense then, or not, as it was. Read it every waking hour I could spare and got through it rather quickly, considering the size of the beast. Didn't get the book fatigue I usually get two thirds of the way through, and would happily re-read it once I get chance (one day, one day).