Google did a great job with Google Maps from developers point of view. Recent V3 version of Maps API is very simple to use in projects. Recently I created an example how to embed map on the site and display custom markers on it. Markers handle mouse onClick event as well.
This example is using Google Maps API Version 3. You can see the result below.
Custom marker example
Markers have mouse click support. Aren't these little penguins cute ? Try to find all of them ), they handle clicks as well.
Google maps custom marker code
Do not forget to include Google Maps API into your page