A nice discussion of some important points needed by those callling to Islam
Source: http://www.islamhouse.com/p/1243
The Importance of the issue of ijtihad, who has the right to make it, and caution of speaking about the religion without knowledge
Author: Salman Bin Fahad al-Awdah
Publisher: http://www.islamtoday.net - Islam Today Website
Source: http://www.islamhouse.com/p/1403
50 Questions And Answers On Islamic Monotheism which talks about Who is your Rub? What is your religion?, Where is Allah?, Who are the friends of Allah? and etc.
Author: Muhammad Bin Abdul Wahhab
Reveiwers: Muhammad AbdulRaoof
Publisher: A Dawah website Wathakker www.wathakker.net
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Author: Zakir Naik
By Shaykhul-Islaam Ibn Taymiyyah. Actions are distinguished, one from the other, with respect to their excellence in the Sight of Allaah in accordance with the condition of the heart, not by their number or form, but rather due to the strength of the caller, his truthfulness, his sincerity and the extent to which he prefer Allaah over himself…
Author: Sheikh-ul-Islam ibn Taymiyyah
This treatise was prepared by the Agency of Islamic Enlightenment in Hajj. Includes a discussion about those things which nullify a person's Islam as well as common errors made by the commonfolk.
Author: Muhammad ibn Saleh al-Othaimeen
Source: http://www.islamhouse.com/p/1377