Fear not.  Your search is over.  For some reason it is hard to find much less navigate to this part of Google’s dashboard.  So here’s some easy instructions.

Get a new Console key from https://code.google.com/apis/console as described in the Version 3 docs at https://developers.google.com/maps/documentation/javascript/tutorial#api_key. Console keys work with Version 2 and provide the benefits of statistics reporting.

It’s against the Terms to use the API without a key, and in fact this won’t work on domains which aren’t Google’s like http://codethink.no-ip.org/mapHacks.html. The webcache version of that page works because it’s on a Google domain.