US GeoDATA  USGS site that archives free DEM (digital elevation model), DLG (digital line graph), and LULC (Land Use and Land Cover) data.  Also includes several links to public domain GIS software.

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.

BOC MSDS Online  MSDS sheets available for download - in PDF format.

MSDS Database  Over 325,000 MSDS 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.