[fish314]

Depends on what you're looking for. For a pretty good series of books about all sorts of aviation topics try The Proficient Pilot, by Barry Schiff. I've only read vol. 1, but he explains complicated concepts with very simple explanations and very little math. He does kind of jump around at times, though and he covers some concepts that many pilots might find esoteric or of little value (like pressure pattern navigation). Overall, a very good book.
If you are looking for a more in depth look, I get some of the information that I post here from looking through my old textbooks (I was an aero engineering major way back when), and some of it I get through my old ground school stuff from USAF pilot training and from my ground school in Tankers and Tweets.
And then, of course, I also reference the old standby's of the FAR/AIM, the Airplane Flying Handbook, the Instrument Flying Handbook, and the Pilot's Handbook of Aeronautical Knowledge. These are awesome, but aren't always the best written or the clearest. But since these are the ones written by the FAA they're must have references.