Sites using data visualization techniques to present their data:
The Winds of the World. This is one of the very best. HUGE amounts of data rendered into an instantly-understandable format. Plus it's beautiful. Click-and-hold to rotate, double-click to zoom in. Let me know if you figure out reverse-zoom. And click on bottom left corner items for more info.
Live Air Traffic is vastly more interesting and informative than giant tables of data.
Scientific Collaborations. I'm not sure what this chart shows, but it sure is beautiful!
US Unemployment, 1976 - 2014. Certainly not the prettiest example, and fairly simple—but brilliantly effective in communicating.
Sites about data visualization or those with multiple examples:
"Data Is Beautiful is a hidden gem for gorgeous data visualizations"