Esri is promoting a new web service enabling anyone to access a wealth of multi-spectral, temporal data to visualize change on planet Earth. Anyone can measure change and analyze the impacts of humans on planet Earth using this innovative, fast web service. The resource takes advantage of a new technology that Esri refers to as Image Services. See more on Twitter via #ChangeMatters or jump to the service at http://www.esri.com/landsat-imagery/index.html
For details on development of the service see this blog post from Dave Bouwman
See Also: Change Matters Tips – information about the image services, things to look out for in the imagery