David McNamee, one of the pioneers of risk-based auditing, published a book in 1997, Risk-based auditing, most of which is still relevant, but may not be easy to find. Part of the structure of my audit database is the same as a table that he suggested for audit testing, so I must have got something right! His books are available from the IIA bookstore. (Also try a search on “David McNamee audit books”).
The non-designers design book(4th edition), Robin Williams, Peachpit Press. Not an internal audit book but one which is very important when much of our final product is “written” – even if this is a “Word” document, “PowerPoint” presentation, or web page. Do the reports from your department look boring? Then get reading. Check out her other design books for ideas.