Fiction:
Daughter of the Empire / Servant of the Empire / Mistress of the Empire trilogy by Raymond. E Feist http://uk.ask.com/wiki/Daughter_of_the_Empire?lang=en
Very well written and I found it gripping. Lots of fantasy based magic stuff but the plot and the clever way the lead character solves her challenges is what makes the story so good.
There is another series written by the same author that fits well along side this - the
Riftwar series, centering on the fortunes of a Magician-in-training. This was written first I believe and is also very good, but for me not quite so good as the Empire series. Both work as stand alone series.
Battlefield Earth by L. Ron Hubbard is also a very good read. It's not all about war as the title suggests but there is indeed a lot going on there and it just gets better the more you get into it.
http://uk.ask.com/wiki/Battlefield_Earth_(novel)?lang=en Again it's very well written, with clever plot lines and out-thinking going on....
Don't watch the film - it's absolute pants.
Currently I'm on the
Wheel of Time series by Robert Jordan. So far so good, and I hear it gets very complicated, but I'm not very far through it yet
. It was meant to be a decology and each book is quite large in it's own right, but it grew to a series of 15, so it's taken me a long time to pluck up the oomph to get stuck into it as I know it will take me ages to go through it! It's very enjoyable so far though
For non fiction
I like
Theodore Gray's books, especially Elements Vault,
http://www.periodictable.com/index.html
but there's also a really good little book called
'What If' which gives serious but humerous answers to daft and generally impossible questions/scenarios.