National/International Agencies:
USGS EPA DOE USBR
USGS Groundwater Page
USGS, National Water Quality Assessment Program
USGS, Groundwater Modeling Software
USGS, Manual for the Collection of Water Quality Data
USGS, Groundwater Atlas for the U.S.
USGS, Interactive Educational Material on Water and Groundwater
USGS, Techniques for Water Resources Investigations
USGS, National Field Manual for Collection of Water Quality Data
EPA, Office for Groundwater & Drinking Water
EPA, Center for Subsurface Modeling Support
EPA, Software for Environmental Awareness
EPA, USDA: Proposed Guidelines, Animal Feeding Operations
EPA, USDA: Joint Statement on TMDL related Ag Issues, 5/2000
EPA, Atlas of America's Polluted Waters
EPA Ag Center
EPA Watershed Central
International Hydrological Programme (UNESCO): Publications
U.S. Salinity Laboratory Modeling Support
USDA-NRCS Technical References (Soils Handbook, etc.)
USDA-NRCS Animal Waste Management
USDA Online National Agricultural Library (water & agriculture titles, online)
The National Academies' Water Information Center
UNESCO Water Portal
UNESCO World Groundwater Map / Hydrogeological Map on the Web
FAO Water (global water resources in food production)
The World's Water (Biennial Report with Data, Pacific Institute)
Global hydrological data resources
World Bank Groundwater Management Team (GW-MATE) Briefings (Factsheets)

National Professional Organizations:
American Geophysical Union (AGU) - Hydrology Section
National Ground Water Association (NGWA)
American Water Resources Association (AWRA)

News, Outreach, and Blogs:
US Water News
Water Tech Online
Groundwater Foundation
Volunteer Monitor, National Newsletter of Volunteer Water Quality Monitoring
American Groundwater Trust
National Ground Water Research and Education Foundation (NGWERF)
Aquafornia - California Water News online (Water Education Foundation)
Circle of Blue - global daily water news, video reports
Waterwired - Michael Campana's Water Blog (great daily writing water blog)
Crickey Creek - another blogsite with links to more water blogs (right hand column)
Hydrology, Hydraulics, Water Quality (HHWQ) modeling resources blog

Video based Water Information & Water Talks:
California Colloquium on Water (Videos; UC Water Resources Center Archives)
UC Davis "Land, Air, and Water Resources Centennial Speaker Series"
UC Davis Groundwater Video Blogs

Other Interesting Groundwater Sites:
 Groundwater Modeling Resources
Vadose Zone Modeling Resources
Well Owner Information, Education, and Resources (through NGWA)
Hydrology Related Web Sites (through AGU)
The Hydrologic Cycle - A Basic Introduction
Your Water Footprint - Calculator, Background, Publications (Water Footprint Network)
Nitrate and the "Blue Baby Syndrome" (WSU Agrichemical and Environmental News)
Nitrate in groundwater FAQ; (Santa Clara Valley Water District)
WSU Pesticide Information Center On-Line
Toxicological Profiles of Hazardous Substances (ATSDR)
EPA's Groundwater Primer on the Web
Water-related Pseudo-Science - Links and Information
Ken Bannister's Groundwater Page
Richard Winston's Groundwater Modeling Page
Interactive Groundwater Flow and Transport Models (Univ. of Illinois)
Smith-Comesky Ground Water Science
The Hydrogeologist's Homepage
Educational (Music-)Video Animation about Groundwater (King County, WA)
Soil Water Monitoring and Measurement Booklet
A Ready Reference for Irrigation, Manual of Practice
Assessing the TMDL Approach to Water Quality Mgmt (Nat. Research Council Report)
USDA ARS - National Watershed Database (STEWARDS)
NGWA 2002 McEllhiney Lecturer: John H. Schnieders (Well Rehabilitation)
University of California, Davis, Groundwater Modeling Weblinks

Resources for Educators:
The Educator Toolbox (Watersheds, Water Quality; Stormwatercoalition.org)
Ploppy: Groundwater Webpage for Children (in Spanish)
Project Wet - Worldwide Water Education - Groundwater
Your Water Footprint - Calculator, Background, Publications (Water Footprint Network)

Christmas 2004 Indian Ocean Tsunami disaster - groundwater impacts:
UK Groundwater Forum
International Groundwater Resources Assessment Center