One of the Fighter options in the PnP game is a shield attack. I used it a few times in a game.
As for adding special animations for shield blocking, if it can be done and not affect the frame-rate or AI then fine. However, I'm happy as it is because, as others have said, D&D has never specified which part of the AC it is that prevents an attack from landing. Combat in D&D drags out long enough as it is, I don't want to have to consult another table to see whether it was my armour, DEX, magical protection, Dodge, natural armour, or shield that helped.
