Go to the source - FEMA Federal Emergency Management Agency MAP Service Center http://msc.fema.gov/webapp/wcs/stores/servlet/FemaWelcomeVie
Want to know about whether your specific property is in a flood zone? You can ask your insurance agent to check that for you or you can use a serivce to get your Natural Hazard Report. A couple of companies who does that are NHD Reprot http://www.Nhdreport.com and JCP report http://www.JCpreports.com
The "100-year flood" zone means that the area's elevation has a 1% chance of being equaled or exceeded by flooding each year, or a 26% chance of suffering flood damage during the term of a 30-year mortgage.
The "500-year flood" zone means that the area has a lower risk of flooding. However, 25% of all flood insurance claims are from these areas.