I didn't wake up this morning expecting to be psyched up about a weather webpage, and yet here I am... psyched about The Weather Channel's use of Microsoft's Virtual Earth
While most TV stations still use animated gifs of their weather radar, The Weather Channel has constructed a mashup that lets you overlay weather radar and/or cloud cover data over the entire US. You can even zoom in/out and drag around, to see where your local storm starts and stops.
An animation feature "plays" the last hour of data on the map so you can see which direction the storm is going. You also have a slider to set the opacity of the overlays. Definitely the coolest weather map on the Internet.