Wikimapia is the perfect combination of Wikipedia and Google Maps.

Labeling the name, purpose, owner, and interesting history of a building on Google Maps is what makes Wikimapia so cool. Thanks to Google's API, users can annotate any building on the map themselves, including their own home or school, and share with everyone the large and amazing buildings they've found, without having to go through the trouble of searching for Google Earth's landmark files.

It fully adopts the Wiki self-service entry mode and supports Chinese, although there are few landmarks in mainland China (including Hong Kong). There is one downside: it loads a bit slower than Google Maps, hehe.