This is a great animation of 'stuff' in the air: blue = sea salt, green = organics, red/brown = dust, and white = sulfates. What these things are and how they become aerosols is an interesting story, but even without that this animation beautifully illustrates the main wind bands around the planet.
Well, I'm not that impressed USGS - your animation looks 'cool', but how about telling us what these colors mean? The colors appear to indicate thickness of deposit - somehow.
Esri Demographics is a nice interactive web map showing you what demographic data Esri has available for you for different countries around the world. It's not quite clear how you would access those data, but the little Map image in the pop-up is nice as a short-cut to available ArcGIS Online map layers.
This looks great: Tabula is a simple and free tool to extract tabular data from PDF files into CSV format - that's it. There is more information about Tabula on the Source.
This is cool (in theory): The Live Boston Train Map.
Lot's of content and lot's of customization, but somehow the look and the feel of this web map don't work for me.