These are some great books I have in my collection. Care to add?
The little white book on top is "Flatland" by Edwin A. Abbott

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Anyone else post some good ones?
Fine. I guess nobody reads anymore anyways....

I'm not particularly clear what kind of texts you might lump into these various categories. I'll give it a shot at any rate.

In the Time Travel grouping I would have to include, although it is fictional, Kurt Vonnegut's Timequake.

Philosophies--what a massive collection. Plato's Republic is a great read. I really liked Book X on mimesis which was nicely debated by Aristotle some years later. While I don't agree with Plato he does make some really sound logical steps. Which I dig. ;)

Zen and the Art of Motorcycle Maintenance is hands down my favourite philosophy book. Pirsig is a genius.

Multiple Dimensions & Universes. That's a tough one. You've listed the books that I also enjoyed (Kaku, Hawking, and Abbott). I remember picking up Flatland at my local library and wondering what on Earth it was. If I remember correctly I was 12 years old and the text had been rebound and not labelled. What an awesome book. At the moment I can't think of anything to add to this that is strictly fitting to the scientific definition. I'll let it sit for a while.

There are far too many books that could be added into these for me to list. I've got to get back to the text I was reading before I took my little "break" for interweb time. It is called Differance by Jacques Derrida. Good read.

Godel, Escher, Bach: An Eternal Golden Braid is a good one, but it's probably the heaviest book I've ever read. Not something you can just sit down with and read cover-to-cover.

Sphereland (written as a sequel to Flatland).

Possibly the single most formative book for me growing up was The Mind's I

The Cat in the Hat is pretty trippy.

Carlos Castaneda's books were really popular for many years. Probably still are with many people. Journey to Ixtlan, and two others put him on the map.

This quote just coughed up with a quick Google, hmmm, very glad I found this at this time.

Journey to Ixtlan.

There is no need for us to say anything about others. There is no need for you or for me to regard other's actions in our thoughts one way or another. The worst thing we can do is to force people to agree with us. I mean that we shouldn't try to impose our will when people don't behave the way we want them to. The worst thing one can do is to confront human beings bluntly. A warrior proceeds strategically. If one wants to stop our fellow men one must always be outside the circle that presses them. That way one can always direct the pressure.
      * * *
      Fright never injures anyone.
      * * *
      What injures the spirit is having someone always on your back, beating you, telling you what to do and what not to do.
     
      People hardly ever realize that we can cut anything from our lives, any time, just like that. For example, smoking and drinking are nothing. Nothing at all if we want to drop them. Only one thing is indispensable for anything we do; the spirit. One can't do without the spirit.

Douglas Adams!! specifically these five by him:

The Hitchhiker's Guide to the Galaxy
The Restaurant at the End of the Universe
Life, the Universe, and Everything
So Long, and Thanks for All the Fish
Mostly Harmless

they are laugh out loud funny - i have read The Hitchhiker's Guide to the Galaxy a few times (5 or 6 maybe?) and it makes me smile so much that by the end of the book the sides of my mouth hurt