As several people have already recommended I think "Eisenhorn" is a fantastic Warhammer 40k book and is a pretty good place to start.

I also really enjoyed the Word Bearers series, which begins with "Dark Apostle", if you would like to dig into the corrupt world of Chaos Space Marines.

Over on my blog I have actually made a list of suggestions for new readers, which you might want to check out: Suggestions for new 40k Readers

What is the best place to start Warhammer 40k?
Uploaded the files, saw it in design, put it as active today.  Cleared the cache and it didn't show, then disable the cache and it still pointing to /default vs. pt003
