1ed Dungeons and Dragons
There were three shields presented: Large, Medium, and Small, although the item listing provided costs for Large, Small, and Small wooden. All three shields were basically treated the same. Shields gave an effective armor bonus of 1. The only difference was that Large shields protected against only 3 attacks a round, medium only 2, and a small shield only 1.
3ed Dungeons and Dragons
There are six shields presented: Buckler, large steel, large wooden, small steel, small wooden, and tower shield (the poor medium shield is still neglected). They each have their own uses. Small and large shields can be used as bashing weapons, and rules for adding spikes are present to make them more dangerous for such tasks (if you consider a d6 damage and times 2 critical dangerous).