The book has been dubbed "mommy porn," as it has attracted the likes of many middle-aged, married women.

"It's completely and utterly overwhelming," James, whose real name is Erika Mitchell, told the Daily Mail of her success. "I just wanted to tell a rollicking good story -- peppered with lots of sex. I always had vague hopes of being published, but everyone always tells you it won't happen."

"When you fall in love, you have a lot of sex," she said, adding "at least from what I remember. 'My book is a guilty pleasure."

James describes her novel as a "romantic fantasy story" that offers women a "holiday" from their husbands and every-day lives. The book's main characters, Christian Grey and Anastasia Steel, were inspired by "Twilight" characters Edward Cullen and Bella Swan.

So, it's no wonder that the "Fifty Shades of Grey" secured a multi-million dollar movie deal, in the neighborhood of $5 million, according toEntertainment Weekly.

Casting for the movie has already caused a buzz, despite the fact that no solid offers have been made. Many young Hollywood heartthrobs and starlets are rumored to be in the running for the coveted leading roles.

We compiled a list of names suggested to play Grey and Steel. Who do you think should play the steamy couple? Check out our slideshow then take our poll below.