I really should at least mention the hard work Frank Taylor from gearthblog.com has put into getting Blue Marble Imagry to overlay on your Google Earth Globe. The results are amazing, it seems a definite improvement over the patchwork mosaic you see when viewing large areas, and as a bonus you get realtimeish (3hours) global clouds.
Anyway read more over at GEarthBlog, here.
Or just download directly here .
(it exploits the new Region Functionality in the GE v4 (Beta), however a bug prevents this from working nicely in all but the very latest version, so such users fall over gracefully to a version that works by intereacting with a webserver. )