This Thursday, May 24th at 9:00PM EST, Hollywood Memorabilia will be listing a Death Star surface panel, measuring 23.75-inches x 11.75-inches, used in the filming of 
A New Hope. 
This screen-used piece of 
Star Wars history is accompanied by two letters of authenticity from 
Lorne Peterson and 
Jonathan Erland. 
Follow this link for 
more information.

For a little bit more information on these surface panels, have a look at 
Ron Salvatore's article on the Star Wars Collectors Archive.