Geograhpy Hierarch setup, address clean up, and ZIP4 product

The University of Virginia needs to clean up existing customer address data.  We're on R12 and considering how best to use the Geography Hierarchy functionality.  I've come across an inexpensive source of address data from the Semaphore Corporation called ZIP4.  They advertise that dozens of Universities have bought the data.  Is anyone here familiar with ZIP4 or any other sources of address data and address validation data?

Thanks

Wayne