Environment Canada is nice enough to publish radar data for their many weather radars across the country. The Exeter WSO radar covers the area in which I live.

A friend of mine has created a great Google maps mashup which makes use of the data provided by Environment Canada in combination with the KML file format which has recently been standarized. Note that because of the multiple overlay layers you may need to turn off some of the data (checkboxes on the right) to make Google maps faster.

Environment Canada Weather Radar on Google Maps

Environment Canada Weather Radar KMZ (Google Earth)

Kier has also made a couple of blog posts describing the development of the mashup [1, 2].