InfoUSA is a great source for this type of information. Beyond zip codes and area, you could filter buy number of employees, years in business and even the type of Business based upon SIC codes. This is useful if you have built an application that targets a certain demographic, or client type.
For example, lets say you built SALON software. You could use infousa to get a list of hair salons that have 4+ employees in the states where you want to target. Very smart marketing when combined with Email, Direct Mail, Phone and even in person sales visits.
Best of luck.