Godel, Escher, Bach by Douglas Hofstader
I've always found GEB easy enough to read; it's understanding[0] it that takes some effort.
For instance, it wasn't until recently running across a handholding explanation of the slogan "syntax and semantics are adjoint"[1] that I've felt I've finally digested much of what he wrote concerning Formal Systems...
-Dave
[0] 6581840dnP
[1] Smith, "The Galois Connection between Syntax and Semantics",
http://www.logicmatters.net/resources/pdfs/Galois.pdf
