Although Nasa has a download for the Blue Marble at a pretty high res ( I got mine when it was available at 52K x 26K ) this site has a free download for the earth at 180K x 90K or thereabouts

http://www.unearthedoutdoors.net/glo...arble/download

Its done in tiles of 21K square. You can get a 8x4 set or a 16x8 set.

They can sell you higher so the data exists at up to 256x128 tiles or 5M x 2.5M pixels. Thats a big image at 10 terrapixels or about a 1/3 mile long print at 300dpi heh heh...