James L. Halperin's
The Truth Machine is probably the best science fiction book I have read.
H.G. Wells'
The Time Machine is another excellent science fiction book, although the book has been ruined many times by various movies. I would be very interested in seeing a nice accurate interpretation of the book. I also recommend the
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I have to agree with menace on Dante's work, although I must also recommend the entire
Divine Comedy (including the Inferno, Pergatorio, and Paradiso). I lecture on the medieval world often, and it's a great look into the social, political, and spiritual world of the Middle Ages.
I'm currently rereading
the Hobbit, which I do every few years. As well as
R.W. Southern's The Making of the Middle Ages which is an excellent look into the major characteristics of the Middle Ages.
There's also the
Hitchhiker's Guide to the Galaxy, which is a pillar of every gamer/geek's library. Some of Douglas Adams' other work is also quite good (if you like his style; try
the Dirk Gently series).