Atlas Games has a book Occult Lore out that has a great section on oneeromancy, or dream magic, and has great (perhaps the best I have seen) rules and adventure suggestions for adventuring inside dreams, giving characters a certain amount of dream points to manipulate the dream. There are a few templates for dream creatures- manifestations of the id, ego, and superego (as per the Freudian concepts of the mind) and even a dream lich.
Also of interest is the 2E Ravenloft boxed set the Nightmare Lands detailing a strange domain ruled by the Nightmare Man and his Nightmare Court, which live off of inspiring fear into the inhabitants of Ravenloft and the Prime Material Plane. Great for archvillains for a campaign in the dream world.
I also think that the Manual of the Planes and the corresponding Dragon that went with it has information on the Dream Plane and alternate dream planes too.