Geo Data in general is more than just maps, it describes objects and relations in space. Geo-data has wide range of applications.
Here is the list of six sites which provide geo data.
OpenGeoportal.org is a collaborative effort to share resources and best practices in the areas of application development, metadata, data sharing, data licensing, and data sources in support of geospatial data repositories.The project’s code repository is hosted on github. Documentation can be found here.
At sharegeo one can search for geospatial datasets by defining a search box on a map. Click on an item, title to view its metadata and download the dataset.
Download a free Wheelmap app or use the site map and mark the places in your neighborhood as to whether or not they are accessible for people with wheelchairs, walking aids or baby carriages. By clicking on the position localization an individual will see the places in their vicinity.
GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. Designed for interoperability, it publishes data from any major spatial data source using open standards. They provide a comprehensive guide to all aspects of using GeoServer. Documentation can be found here.
The GeoNames geographical database is available for download free of charge under a creative commons attribution license. It contains over 10 million geographical names and consists of over 9 million unique features whereof 2.8 million populated places and 5.5 million alternate names. All features are categorized into one out of nine feature classes and further subcategorized into one out of 645 feature codes. The data is accessible for free of charge through a number of web services and a daily database export. GeoNames is already serving up to over 150 million web service requests per day.GeoNames has a simple edit interface that allow users to edit GeoNames information, move a point and add new place names to the GeoNames database. Documentation can be found here.
Google Earth is a geobrowser that accesses satellite and aerial imagery, ocean bathymetry, and other geographic data over the internet to represent the Earth as a three-dimensional globe. Google also refers to Google Earth as a "geographic browser." The Google Earth plug-in allows you to navigate and explore geographic data on a 3D globe using a web browser. The Google Earth Plugin is currently only available on Windows and Mac OS X 10.6+.
This is compiled by Megter.