This book gives a clear explanation of the Muslim sound Creed which is the core of the religion of Islam, as the belief in Tawhid (monotheism) is the purpose for which Allah created both mankind and jinn, and thus, those whoes belief in Tawhid is corrupt, are not considered Muslims.
Author: Saleh Bin Fawzaan al-Fawzaan
The Fatawa's of Shaikh-ul-Islam Ibn Taymiyyah (Rahimahullah). Though he preferred the Hanbali school of jurisprudence, he was never biased in favor of it, he frequently quotes the opinions of all four of the well-known schools of jurisprudence, even others. In a number of matters, he himself held opinions different from those of the four schools.
Author: Sheikh-ul-Islam ibn Taymiyyah
This book, The Religion of Truth, treats these basic and great subjects. We should know that the only way for our salvation in this life and in the hereafter is to know, for sure, our Lord who created us, believe in Him, and worship Him Alone. We should also know our prophet whom Allah had sent to us and to mankind, believe in Him and follow him. We should know the Religion of Truth which our Lord has commanded us to believe in and practice it.
Author: Abdurrahman bin Hammad Alomar
A nice discussion of some important points needed by those callling to Islam
Source: http://www.islamhouse.com/p/1243
The Choice - Islam and Christianity: Two Volumes, By Ahmed Deedat, An excellent book discussing Islam and Christianity in the light of Holy Quran and the Sunnah.
Author: Ahmed Deedat
A small treatise concern knowledge & scholars, its importance & merits.
Author: Abdul Aziz bin Abdullah bin Baz
Publisher: http://www.al-hidaayah.co.uk - Al-Hidaayah Publishing and Distribution Website
Source: http://www.islamhouse.com/p/1257