Wikimapia, which is basically wikipedia plus location, just added the ability to embed maps into your page. I like the neighborhood boxes and the map interface, but as far as labeling and tying together the world, it’s not quite as good as 43 Places, which lets users map their neighborhoods with more precision than a rectangle.
The amount of open, user generated spatial information on the web is skyrocketing right now.
I am agreeing with you about the usefulness of 43Places. It is a great site where you can drive around the map and see the placemarks. In addition, it has a new feature- Events- that let you see what is going on at a place. It is very funny to explore the site.