"Income Tax Regulations" is a six-volume series that comprehensively discusses the IRS tax code and proposed regulations. The book was produced by CCH Tax Law Editors and is considered a standard reference for tax professionals. It includes a full text reproduction of the official federal income tax regulations.
Grover Norquist's "End the IRS Before It Ends Us: How to Restore a Low Tax, High Growth, Wealthy America" is a political commentary that discusses the IRS tax code, analyzes the problems within the agency, and presents solutions to reform the tax code. The book was published by Center Street in 2015.
Another interesting book with a religious point of view is Mark Emery's "How I Beat Satan and the IRS," published in 2015 by PFC World Mission, LLC. The book is a short, non-technical discussion of how Christians can attempt to reconcile their obedience to God's Law with the seemingly conflicting laws of the IRS tax code.
A book that discusses the tax code from the perspective of an IRS employee is Richard Yancey's memoir "Confessions of a Tax Collector: One Man's Tour of Duty Inside the IRS." Published in 2004 by Harper, this book recounts Yancey's experiences as a field officer for three years with the Internal Revenue Service.