Ohio Geographically Referenced Information Program
http://www.state.oh.us/ogrip/

OEPA GIS Data
http://www.epa.state.oh.us/dsw/gis/index.html

(ESRI)Environmental Systems Research Institute, Inc
http://www.esri.com

United States Geological Survey, National Mapping Information
http://mapping.usgs.gov

United States Geological Survey, Water Resources of the United States
http://water.usgs.gov

United States Geological Survey, Guide to Downloadable Digital Data
http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html

The Ohio State University, Center for Mapping
http://www.cfm.ohio-state.edu/