A collection of 1K and 2K JPEG surface texture maps of Mars is now available at http://www.lns.cornell.edu/~seb/celestia/mars-maps.zip It's about 5.5MegaBytes.
They're described on the Web page http://www.lns.cornell.edu/~seb/celestia/gallery-002.html
These maps have been available individually for quite some time, but I decided it'd be appropriate to make them available as a single download which includes the necessary AltSurface SSC catalog.