This well-researched and exhaustive biography on screen legend Marilyn Monroe by Donald Spoto (who passed away this past February) was released back in 1993. While he doesn't wallow in the gossip and speculation that surrounded her, he does debunk many of these myths.
Marilyn's career spanned 16 years & 29 films and while I would have liked more behind-the-scenes of her films, I definitely came away respecting her even more than I did before.