Screen Capture from Wikimapia
Wikimapia is an online editable map - you can describe any place on Earth. The map details everything from regions to business parks, shopping centers, industrial parks... basically, if you can pin it on a map, Wikimapia gives you the ability to add something about it.
It looks like there are two ways to add info to the map.
• Add a wiki-style description.
• Add comments.
The mapping tool looks useful for both researching properties AND adding your own information. So if you represent a building, consider adding a comment saying so.