The FEMA Map Center is a good resource for many types of digital maps including FEMA issued flood maps, flood insurance studies (FISs), and flood insurance rate maps, both paper and digital (FIRMs and DFIRMs, respectively).

You can find a list of links to all the products the Mapping Service Center provides on the FEMA product page. While not all of these resources are available free, much of the data for use in geographic information systems (GIS) is downloadable at no cost.