Here is a filled circle overlay for use with Google Maps. It uses plain html only, no canvas, svg or vml.
It should work with all browsers.
This is a scaled filled circle overlay using HTML only. Radius is give in meters. The fill of the circle can have a
selected colour and opacity. The big circle is 1km in radius and the small 500m. Firefox will stop rendering the
circle when its equivalent font size goes beyond 2000px, other browsers will render large circles.
The circle provides mouseover, mouseout and click events, though these will not work well if there are overlapping circles on the map.
Source code for the Filled Circle Overlay is
here.