Stephen Bullen, Rob Bovey, John Green , "Professional Excel Development" (repost)

Finally, there's a book that treats Excel as the powerful development platform it really is, and covers every facet of developing commercial-quality Excel applications. This is not a book for beginners. Writing for professional developers and true Excel experts, the authors share insider's knowledge they've acquired building Excel applications for many of the world's largest companies — including Microsoft. Professional Excel Development demonstrates how to get the utmost from Excel, addressing everything from application architectures through worksheet and userform design, charting, debugging, error handling and optimizing performance.