ArcGIS Online http://www.esri.com/software/arcgis/arcgisonline/index.html "ArcGIS Online Services provides free, ready-to-use content and capabilities for ArcGIS users including 2D maps, 3D globes, reference layers, and functional tasks.ArcGIS Online Services provides free, ready-to-use content and capabilities for ArcGIS users including 2D maps, 3D globes, reference layers, and functional tasks."
ArcWeb Explorer http://www2.arcwebservices.com/v2006/solutions/awx.jsp "ArcWeb Explorer is a Web application that demonstrates browser-based map rendering. The result is improved speed and performance, greater control over the map appearance, and desktop-like functionality over the Internet. In addition to mapping streets, data, and imagery, ArcWeb Explorer exposes other ArcWeb Services functionality through various easy-to-use widgets. For example, you can use ArcWeb Explorer to quickly find locations, create driving routes, and generate demographic reports."
Atlas: The Louisiana Statewide GIS http://atlas.lsu.edu/ LSU’s atlas of GIS data. They have a fantastic supply of aerial imagery and other data.
Center for Spatial Analysis at the University of Oklahoma http://www.csa.ou.edu/ "The Center for Spatial Analysis (CSA) at the University of Oklahoma is a multidisciplinary university research center specializing in the study and application of geospatial science and technology."
Data Soruces for GIS http://www.colorado.edu/geography/gcraft/notes/sources/sources_f.html A great article written by Kenneth E. Foote and Margaret Lynch, Department of Geography, University of Texas at Austin, on where to find GIS data.
EPSG Geodetic Parameter Dataset http://www.epsg.org/Geodetic.html The EPSG geodetic parameter dataset is a repository of parameters required to identify coordinates such that those coordinates describe position unambiguously. This is through a coordinate reference system (CRS) definition. And also todefine transformations and conversions that allow coordinates to be changed from one CRS to another CRS. Transformations and conversions are collectively called coordinate operations.
ESRI Data Downloader http://arcdata.esri.com/data_downloader/DataDownloader?part=10200 Zoom to a geographic location and download data for that area, straight for ESRI!
Geography Network http://www.geographynetwork.com/ "Share geographic data and services through a global network of publishers."
H-GAC Geospatial Data Clearinghouse http://www.h-gac.com/rds/gis/clearinghouse/default.aspx The Houston-Galveston Area Council has a great selection of data for the Houston and Galveston area!
Harris County Public Infrastructure Department http://www.eng.hctx.net/gis.htm GIS map libraries and shapefiles of data for Harris County, Texas.
Kansas Geological Survey http://www.kgs.ku.edu/PRS/petroDB.html Energy resources (oil and gas) data from Kansas!
Louisiana Geographic Information Center http://lagic.lsu.edu/ "LAGIC was established by the Louisiana GIS Council (LGISC) and the Louisiana Office of E-Services to facilitate the distribution of geographic information, provide technical assistance, and support GIS data development among state, federal, and local government."
The Map Library http://www.maplibrary.org/ A large resource of aerial imagery and datasets for Africa.
Mississippi Automated Resource Information System (MARIS) http://www.maris.state.ms.us/ This website provides access to Mississippi's statewide geographic information system.
TNRIS (Texas Natural Resources Information System) http://www.tnris.state.tx.us/ TNRIS is an excellent resource for Texas data. From aerial imagery to roads data, they are very useful!
USGS Seamless Data Viewer http://gisdata.usgs.net/website/seamless/viewer.htm Free data downloads, user defined datasets and area, acquire data from different hosts, elevation point and profile tools, and more!