MARTHA has found these GIS sites to be useful:

What is GIS?		Environmental Systems Research Institute, Inc.
		National Center for Geographical Information and Analysis
		University of Waikato, Department of Geography
		Kingston Centre for GIS, Kingston University
		University of Colorado, Department of Geography
		Digital Land Systems Research
GIS Glossary		University of Edinburgh, Department of Geography
		Jefferson County, GIS Department
		BC Ministry of Environment, Lands, and Parks
		Queen's University Digital Map Library
		University of California, Berkeley Library
		Environmental Systems Research Institute, Inc.
GIS Web Sites		The GIS Portal, Great GIS Net Sites Index
		Association for Geographic Information
		GISLinx, Catergorized List of GIS Sites
Other useful stuff!		You can join the Spatial News mailing list here (and also find lots of other useful info on software & data). They also provide a useful list of data translators.
		The GeoCommunity GIS Data Depot Other GIS/Geo Sites
		A wonderful site when looking for GIS data--the Aboriginal Mapping Network Data page.
		A complete list of mailing lists related to GIS is maintained by Bill Thoen. He also maintains a list of GIS and related Journals.
		The unofficial Arc/Info and ArcView Symbols page.
		Odden's Bookmarks--THE source for finding links to everything cartographic (includes GIS sites). A must-see site with over 10,000 links.