That's hard. I have so many favorites, what I list would probably change every time you ask and lean heavily towards what I am reading or have recently read, but I'll type down the first couple that come to mind:

Bible

Lord of the Rings

The Dragon's Prophecy

The Sovereignty of God

Creation Basic's and Beyond

The Global Flood.

The last two I use frequently as references and have read more than once. Sorry, I couldn't reduce to 5.