Out of the Silent Planet (Space Trilogy, Book One) This is the first in a great purposeful sci-fi trilogy.
Space Trilogy 3 Book Set Out of the Silent Planet, Perelandra & That Hideous Strength C.S. Lewis Here is Lewsis' whole purposeful sci-fi trilogy
The Chronicles of Narnia Another great trilogy from Lewis, but this one is purposeful fantasy
The Complete Chronicles of Narnia CD Box Set Another great trilogy from Lewis, but this one is purposeful fantasy
The Lord of the Rings Trilogy Gift Set Another purposeful fantesy. Several metaphorical figures.
Left Behind: A Novel of the Earth's Last Days (Left Behind No. 1) This one would be considered purposeful sci-fi only because it is about the future--but the true future.
Left Behind - The DVD Collection (Left Behind / Left Behind II - Tribulation Force / Left Behind - World at War) This one would be considered purposeful sci-fi only because it is about the future--but the true future.
The Omega Code This one would be considered purposeful sci-fi only because it is about the future--but the true future.
Megiddo - Omega Code 2 This one would be considered purposeful sci-fi only because it is about the future--but the true future
This Present Darkness and Piercing the Darkness This one could be considered purposeful fantasy although it may fit more the horror gere as deals wtih the reality of demons.
Leviathan
Green (The Circle, Book 0: The Beginning and the End)
In the Twinkling of An Eye