The following links will take you to the national mapping agencies of several countires. These are essentially the equivalent to our US Geological Survey. Though there may not be any interactive mapping here, you may be able to locate useful information about available maps. The Library of Congress holds one of the most outstanding map collections. The American Memory project seeks to bring a portion of these materials to the web user.
Subject matter is selective but several projects are of interest.
General subject oriented guide to map collections. The collection consists of approximately 200 maps dating from the 17th century to the present, reflecting early mapping of the areas that would become four National Parks, as well as the parks themselves. The bibliography contains 623 railroad maps of the United States. The Cities and Towns category includes maps that depict individual buildings to panoramic views of large urban areas. These maps record the evolution of cities illustrating the development and nature of economic activities, educational and religious facilities, parks, street patterns and widths, and transportation systems.