40 CFR Environmental Code of Federal Regulations. 

Wisconsin Administrative Code http://www.legis.state.wi.us/rsb/code/codtoc.html

U.S. EPA homepage http://www.epa.gov/

RCRA Online This is the same database the Hotline uses for hazardous waste questions. http://www.epa.gov/rcraonline/

EPA Solid and Hazardous Waste homepage A good stepping off point for solid and hazardous waste questions. http://www.epa.gov/epawaste/index.htm

EPA Technology Transfer If you enjoy the nuts and bolts of air emission management, start here. https://www.epa.gov/technical-air-pollution-resources

EHS Journal  A nice compendium of information related to environmental management, auditing ans sustainability. http://ehsjournal.org

WDNR homepage http://dnr.wi.gov/

Library of Congress http://www.loc.gov/

CEO Express A great site that has hundreds of links arranged by category (none of them are environmental) http://www.ceoexpress.com/

Engineering Toolbox  a reliable source for a variety of information regarding properties of materials, conversions, HVAC and other. http://www.engineeringtoolbox.com