I know some may say that Google Earth is still the best. But sometimes you may get bored with it after playing with it for a while.
Let me introduce you a free online software known as Flash Earth. It is flash-based service which allows you to explore satellite and aerial imagery of the Earth via a zoomable map from several mapping services, including NASA, OpenAerialMap, OpenLayers, Microsoft Virtual Earth, Microsoft VE (labels), Yahoo! Maps and Ask.com Maps.
In the past, Flash Earth supports Google Maps. But currently I am not sure why it is being excluded from the list.
Although Flash Earth is not as powerful as Google Earth, but at least you are being exposed to different mapping sources to view aerial imagery of the Earth.