Breaking Dawn, by Stephenie Meyer
This is the last book in the series. It's great!

Bella and Edward finally get married. On their honnymoon, the shocking truth shows that Bella is pregant! The half vampire, half human baby is ripping Bella apart, from the inside out. She knows that she will not make it out of labor human, but everyone is wondering, will she make it out at all?
All the while, Jacob is preparing himself to lose Bella, but he would rather take her pain than his own. He is certain that if she makes it at all, she will become something that he hates more than anything else. How will she remain his best friend that way? He would rather her dead. He might just get his way.
Bella, Edward, and Jacob all go through the pain and joy of love. The end of this amazing series leaves you wanting more.

The author's website: http://www.stepheniemeyer.com/
Other books in the series:
1.Twilight, by Stephenie Meyer
2.New Moon, by Stephenie Meyer
3.Eclipse, by Stephenie Meyer