An unbiased account based on respected Islamic sources is:



[[ASIN:1596980281 The Truth About Muhammad: Founder of the World's Most Intolerant Religion]]

There exist a great deal of confusion surrounding this historic character, Muhammad. A lot has been said and written. There is a book written in early days of Islam by Ibn Hisham, Sirat al-Nabi, which supposedly gives a good account of Prophet Muhammad.
First let me tell you that this book is not a worthy scholarly work whatsoever.
The author is clearly obsessed with Islam and the character of prophet Muhammad, so no one who is after reading an objective research should expect an unbiased account being produced by this author. He is as subjective as one could possibly get. What you probably get out of this book is no more than what you would get by going to a mosque in your city and listening to a cheap Mullah. Don't waste your time and money on something that you can get on any Islamic website on the net for free.
The best work that I have come across so far is 'Twenty Three years, a study of the prophetic career of Muhammad' authored by Ali Dashti.
Ali Dashti neither was an Islam basher nor an Islam-intoxicated like Nasr nor did he have any political motivations. In his work Dashti uses a wide variety of references, starting from Quran itself, Hadiths, and other important Islamic references.
First I thought to give the Nasr's two stars, but it isn't really worth it.