If you are in the construction trades or building maintenance, these books are a "must-have" to stay on top of the latest regulations. Many cities use the International Codes for the basis of their regulations. These are hot off the press 2009 manuals. They can more than pay for themselves by keeping you out of trouble with the local building inspectors.
If you retrofit buildings, the International Existing Building Code is a must-have reference for your desk. It covers repairs, alterations, additions, and changes in occupancy for existing and historic buildings. This code book encourages use and reuse of existing buildings.