The BBC carried
an article a couple of weeks ago about Wikipedia and suggested that the wiki model followed by Wikipedia might be expanded to include all sorts of things, including maps. This could be an interesting way of producing an up-to-date and accurate geo-spatial data set at a very low cost. Perhaps the form could be similar to
London Free Maps, just on a more global scale.
Try stickymap.com. This website let's you post all kinds of markers on a google-map along with a wiki-style description.