USGS Seamless Data Warehouse  USGS site that archives free NED (National Elevation Dataset) for use in geospatial applications.

GeoDATA  US Goverment site for federal, state and local geographic data.

GIS Data Depot  Contains the above maps as well as some maps no longer available at the USGS site, such as 7.5 minute quad DEM maps and DRG (digital raster graphic).

MapMart  Another great site for DEM data, aerial photography, satellite imagery, and much more

MICRODEM  Offers free software to handle, display and merge electronic maps; also has conversion routines between NAD27 and NAD83 and other world coordinate systems.

Chemical Finder  Chemical database where names and CAS numbers can be cross-referenced, and chemical properties displayed or printed.

Compressed Gas SDS Online  SDS sheets available for download.

SDS Database  Over 325,000 SDS sheets.

North American Industrial Classification System (NAICS)  This site provides codes for industries using the North American Industry Classification System (NAICS). This system has replaced the U.S. Standard Industrial Classification System.

U.S. Standard Industrial Classification (SIC) System.  If still needed, this site also provides SIC codes.