fan-service site The Cult of Rapture has released the fourth and final piece of artwork in their Artists Series. "Subject Delta," seen below, was painted by Boris Vallejo and Julie Bell. It depicts the Big Daddy prototype (code-name: Subject Delta) you'll be playing as in the game. Purty!
To get a high quality, desktop version, head to the Cult of Rapture site: http://www.2kgames.com/cultofrapture/article/borisjuliesubjectdelta