I believe most top level events use DGT sets (timeless pieces) such as these: http://www.chesscentral.com/DGT_Electronic_Chess_Board_Bag_and_Clock_Package_p/dgt-board.htm
These are probably the standard because it's an easy way to transmit the moves to a computer.
I was wondering if anyone knows of a site that has information about the types of sets used in World Championships and other major tournaments over the years. It seems that most of the recent ones use a German Knight type set. What wood is usually used for the dark pieces, Golden Rosewood, or Rosewood? I can't exactly tell from the pictures I've seen. Are ebony or ebonized pieces ever used? When did this type of set become the norm, and what was used over time before that? I've looked around, but it seems pretty hard to find this type of info. Thanks!