My wife of 8 years is leaving me because she has never ever felt any passion for me. I do believe that in her heart it is the truth. No intimacy is happening now. What are the best books out there to develop a spark with your estranged wife?

If this was a serious question (which I doubt) you must know that there is nothing you can learn, after the event, from a book. Even someone as staggeringly clever as me cannot advise.

Try reading the Kamasutra, along with your wife. That'll put a spark in your pants.

After 8 years ... There is NOTHING you can do, except get as friendly a divorce as possible.

Dude.  You had EIGHT YEARS to get your act together.  If you didn't in that time, you won't by reading a book.  Learn the lesson.  Maybe get some relationship counseling, so you know what to do (and not to do) in the future.  But this relationship died a long time ago, and nothing is likely to revive it at this late date.

If there has been no passion there then I'm not sure what you can do. I wonder why she married you in the first place, it seems unfair if you really loved her and the feelings were never mutual? Try a marriage counsellor,  because self-help tips are not going to help here, that would be like sticking a small plaster on a gapping wound.

Most people would suggest you both trying to remember what it was that drew you to eachother eight years ago, but you say she never had any passion for you so that suggestion would be useless.

Two adult human beings are usually capable of having a good marriage.

You and your wife made a commitment 8 years ago.

Require that she honor that commitment.  Seek marriage counseling.