Of course, the Holy Qur'an is my guide to life. Muslims believe that this book was revealed from Allah (God) to Muhammad (peace be upon him) via the angel Gabriel starting from 610CE and ending in 632CE. It's good to read in Arabic. The amazing thing for me is the layers of meaning within the verses; that the more attention you pay to each verse, the more that it reveals.
Of course, one can never do enough Islamic reading. Currently, I am reading Subverting Islam: The Role of Orientalist Centres by Dr A. Ghorab. This would be considered a controversial book, even by Muslims. Its main hypothesis is that so-called "Islamic Studies" centres at western Universities and the like are really nothing more than fronts for agencies intent on destroying the Islamic revival by watering down its message; having failed to do so intellectually and militarily. From what I have read so far, the level of scholarship is high, which makes it hard to dismiss the claims.
There is so much to read about Islam that this section can never claim to be complete. All it can do is highlight what I've read recently and what I have found recently.
I have also read several of Gary Miller's booklets, namely Missionary Christianity and The Amazing Qur'an. The impressive things about these two texts is their brevity (neither is more than 40 pages) and their sharpness. Both are well thought out. What's more, it is written in a style that is easy for people who've grown up with the scientific method and with Western ways of thinking to understand.
For daily reference, I find that The Lawful and Prohibited in Islam by Dr Yusuf Al-Qaradawi is a good handbook. To some extent, he is at times a bit lenient in his interpretation of the Qur'an and Sunnah. However, the material is very accessible. Despite this, the book is somehow banned in France. So much for freedom of speech. Certainly, there's nothing militant about this book, if anything it is not militant enough.
If I have more time, I like to go back to Fiqh-us-Sunnah by Al-Sayyid Sabiq for further details.
Favourite authors are a very subjective thing. Still, I believe these people are practitioners of the art of writing that all people should appreciate. People often shy away from these authors because they are associated with "science-fiction" or "fantasy" realms, but these authors use the domain they are in as a springboard to addressing life in general, and the more interesting parts of being alive. Keep an open mind - and give these authors a fair go.
To be honest, I am losing interest in fiction a little; I only read 4 or 5 fiction books a year now. Don't know why.