If you have a formal systems bent, as I do, you might enjoy "Algebraic Models for Accounting Systems" (http://www.amazon.com/Algebraic-Accounting-Systems-Salvador-...).

"This book describes the construction of algebraic models which represent the operations of the double entry accounting system. It gives a novel, comprehensive, proof based treatment of the topic, using such concepts from abstract algebra as automata, digraphs, monoids and quotient structures."

Think of it as a primer for building yourself an exceedingly awesome and utterly-unnecessary Haskell-based QuickBooks.