Those who have been following the seemingly endless journey of John Carter to the screen will recall that back in 2004 Kerry Conran (director of Sky Pilot and the World of Tomorrow) was attached to direct the film for Paramount when that studio had the rights. It contains a lot of interesting art I haven’t seen before, and gives clues as to where Conran was headed with the project (before he was replaced by Rodriguez, who was replaced by Favreau, who was eventually replaced by Disney and Stanton).
Also I’ve selected some still images from the video. There are some really great concept art images in this video!
UPDATE: As is frequently the case — Bill Hillman at ERBzine was on top of this at the time, many years ago, and has a wonderful couple of pages on it.