I used one of the approaches, Marker Clusterer, recently for a quickie map of 500+ orgs: http://appealforcommunities.org/networkmap http://appealforcommunities

I used one of the approaches, Marker Clusterer, recently for a quickie map of 500+ orgs: http://appealforcommunities.org/networkmap http://appealforcommunities.org/networkmap The InfoWindows were particularly tricky. I wish we could have had the time to do custom marker logos, but the nuclear-like ones work well.