Mapping out the UN Millenium Development Goals is a great feature of this website. If you are not familiar with these goals and indicators, it is worthwhile to become familiar with them.
This is a global map viewer that includes many global datasets and images in a fairly intuitive viewer. I also liked that you can go to the Statistics tab on the left hand navigation Table of Contents, and you can see the UN Millennium Development Goal Indicators mapped. Very straightforward.
Do you like some of the New York Times maps and graphics? If so, you can view some of the projects here. Also, at the bottom of the page is mapShaper, which looks like it could be very useful for simplifying shapefiles for KML use.
This is an interface for doing global or US comparisons of different indicators. Military spending, IKEA, Number of Gold Medals, Crops, Energy, are just some of the indicators that can be mapped.
My impression of this site is "Data 2.0." I like that the data is organized by category, you can upload and download data, and it has graphing capabilities. It could be a little stronger on the mapping aspects, but if you find the data you are looking for here then it is worth it. Also, there may be social aspects to this site that I have not explored yet. Similar to the geocommons finder without the mapping component.
This NYTimes map allows you to explore immigration in the United States over time. It also allows you to choose a country and view data relating to that countries immigrants in the United States.
Are you looking for foreign languages of the world that are in danger of extinction? UNESCO has done an extensive job of mapping and categorizing the world's languages with the aim of cultural preservation.
This web mapping site allows you to view the foreign languages spoken in all 50 states based on Census data, viewable by total, percentage, or zip code.
The Spatial History Project at Stanford University, a part of the Bill Lane Center for the Study of the North American West, is made possible by the generous funding of the Andrew W. Mellon Foundation.