EVGA added a backplate for the GeForce GTX 570 to its product lineup. At $19.99 it looks like a pretty expensive piece of metal though.
The backplate fits onto the reverse side of the PCB, absorbing and radiating some of the card's heat. It also covers up components on the reverse side, making the card look better when installed. Available from EVGA's online store, this piece of brushed metal goes for US $19.99.