My friend gave me the "His Dark Materials" trilogy to read during my maternity leave. I thoroughly enjoyed them, was completely hooked, and some bits made me cry (which may have been attributable to my late pregnancy emotional hormonal state).
The finale of The Amber Spyglass gives a really interesting slant on theology as we know it.
Some Christians hate these books..........
If you enjoyed "The Da Vinci Code", I wouldn't bother trying to read them though!