Here are a few early examples of maps using the new Google Earth for the Browser plug-in. To view these maps you will need to download the plug-in from Google.
Meet Me At
Nearby.org were one of the first with this early demo of an existing Google Map mash-up that now has new and improved Google Earth functionality.
Meet Me At enables two people to arrange a meeting on a Google Map. Choosing your meeting point involves clicking on the map roughly where you would be interested in meeting. If there is already a meeting point nearby, you can pick it up and drag it a small distance, to nudge the point slightly in your direction. The new Google Earth Browser option means you can now view your meeting point in glorious 3d.
GE in a Browser
Also from Nearby.org is GE in a Browser. This map is a great demonstration of Google Earth's features. The map allows you to turn on or off the sun, atmosphere, roads, 3d buildings, terrain. You can even view the Google Sky imagery from Google Earth (Hint: turn on 'On Screen Nav').
Finally you can view 300 videos of tourist destinations around the world by visiting my own Video Earth. Even if you aren't interested in the videos it is a useful map just for viewing all the amazing 3d buildings around the world produced by Google Earth users.
The Glacier Express
Another example of an existing Google Map with added Google Earth Browser functionality is Glacier Express. This map tracks the route of the famous Glacier Express train in Switzerland. Now all the mountains can be viewed in 3d using Google Earth's terrain function.
The terrain option just takes this map into another world.