I know most of you already know of Nasa's "Earth Observatory" project, but for those of you who don't...
http://www.google.com/images?q=earth+observatory&um=1&hl=en&tbs=isch:1,isz:lt,islt:15mp&source=lnt&start=18&ndsp=18
There ya go. Some of the most amazingly high res textures available to folks like you. Enjoy.