Google Maps Mania: Heat Map Creator for Google Maps
GMap HeatMap is a web service from Differential Enterprises for making dynamic heat maps and color contour overlays for Google Maps.
No programming is required to create a heat map using GMap HeatMap. All you require is three columns of data, the latitude, the longitude, and a value. If you paste your data in this form into the HeatMap creator your heat map will be automatically created.