Roger Elwood - AngelWalk Trilogy
really made me think about how evil this world is,the total depravity of mankind and how great the Grace of God truly is.
CS Lewis - The Space Trilogy
Though I have yet to make my way though the third book, the first two are great works and really eye opening on many topics.
John Bunyan - Pilgrim's Progress and Pilgrim's Progress II: Christiana's Journey
Charles G. Colman -The Shining Sword
Both of these works(I count Pilgrim's Progress II as part II and not a seperate story in my mind, though it is) really cause one to examine their own selves and see if indeed they Christians or not....
Bill Myers - Eli, Blood of Heaven, Threshold
I can not describe these too much without spoilers... let's just say this, Scifi, Characters meet or deal with Jesus... lives changed... good stuff.
Also Bill Myers for kids... "My Life as..." or funny stuff happens to Wally McDoogle... just has to be read... and of course "McGee and Me" -- this one had a lot of influence on how I saw the world when I was young and moving a lot... loved both the books and the movies made off them...
and this is just a short list, it's late here, to tired to think of more... will do so later...