Check out http://antwrp.gsfc.nasa.gov/apod/image/0208/marsglobe_viking_big.jpg
This is quite a picture! But can be the first to point at the bottom right hand corner and say "missed a bit!". Still, filling the gaps is justification for another Mars mission in my book. Do you think I'd get a job as budget controller for NASA?
It's a mosaic of Viking images, I think, but impressibe because it's (almost) the whole globe....