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.
Programmers can also drive HeatMap from PHP, with a POST operation, so you can include Gmap HeatMap maps in your own website.