Glenn's Urologic Surgery by Sam D Graham, Thomas E Keane, James F Glenn is a recently updated, excellent text. A surgical atlas is a must have text during residency. If you get one during medical school it could help you significantly during your sub-I. By spending 30 minutes reading the night before the operation, you will look like a star when attendings and residents pick your brain during the surgery.
Urology Secrets by M. I. Resnick, A. C. Novick. If you cannot get through Smith's General Urology or Clinical Manual of Urology, consider reading this book cover to cover. This is a very comprehensive text in quite readable Q&A format that is useful for both pre-rotation reading and for quick topic review
Clinical Manual of Urology by P. M. Hanno, S. B. Malkowicz, A. J. Wein. The pocket-sized volume serves as a fantastic reference manual for both the clinics and the wards. This text can easily substitute for Smith's. Whether you need a quick refresher course on renal cell carcinoma before a case or trying to figure out how to free penile skin from a zipper in the ER--this text will bail you out. Certainly a must for every resident. This new edition came out in May 2007 as a companion text to Cambell's.
Smith's General Urology by E. A. Tanagho, J. W. McAnich. This text is a very comprehensive overview of urology and is probably the basic text most commonly used by both students and residents. It is a good textbook for medical students to try to finish before beginning a sub-I. It also serves as a good intro book to read during your general surgery internship.