Where can i download a good World image in GeoTIFF?

I was able to georeference an xglobe image using gdal_translate

gdal_translate -a_srs WGS84 -a_ullr -180 +90 +180 -90 xglobe-2400.jpg xglobe-2400.tiff

http://visibleearth.nasa.gov/view.php?id=57752

...and pick your resolution with images from 2MB to 401MB

Natural Earth offers free vector and raster map data at 1:10m, 1:50m, and 1:110m scales.

For example: global satellite-derived land cover data (.tif file) and shaded relief available with ocean bottom data, or without.