Gödel
Godel's incompleteness theorems are fundamental to understanding the limits of scientific and mathematical knowledge and the power of self-reference.
Gödel, Escher, Bach should be considered required reading for a full understanding of metaculture.
Here's a basic explanation of Gödel's incompleteness theorem if such a thing exists.
A free online course from MIT is available to help get the most out of this seminal work.
Technically this is based on another book by Hofstadter but it does a good job explaining a lot of the concepts of recursion and consciousness that are in GEB.