Kitab At-Tawheed is one of the best books on the subject of Tawheed (Islamic Monotheism) and ranks high in authenticity. Till date it has gone through various publications; and had been the means for guidance of the millions of people throughout the world; by taking them out of the darkness of polytheism and error.
Author: Muhammad Bin Abdul Wahhab
Publisher: http://www.islambasics.com - Islam Basics Website
Praying 'Eid in the Musallaa is the Sunnah: there is great and profound wisdom behind this Sunnah – the Sunnah of praying in an open area of land. And it is that: The Muslims will have two days of the year where all the people of every city can gather together – whether men, women or children - and turn towards Allaah with their hearts in unity, praying behind one Imaam, making the Takbeer, the Tahleel and supplicating to Allaah sincerely together, as if they were united upon the heart of one man, happy and joyous about the blessing Allaah has bestowed on them. So the Eid will truly be an occasion of celebration for them.
Author: Muhammad Naasiruddeen al-Albaanee
Translators: Abu Maryam Ismaeel Alarcon
An excellent book for non-Muslims explaining various aspects of Islam.
Author: Pete Seda
Publisher: Islamic Propagation Office in Rabwah
Source: http://www.islamhouse.com/p/1301
Ibn Taymiyyah said: "This (enjoining good and forbidding evil) is a duty that the entire Ummah is obliged to fulfil. It is what the Ulama know as an obligation of collective responsibility, if a group in society undertook to discharge it, the other members of this society are absolved from it. The entire Ummah is commissioned to undertake it, but if a group therein was responsible for discharging it, the rest of society is no longer obliged to undertake it."
Author: Sheikh-ul-Islam ibn Taymiyyah
Reveiwers: Muhammad AbdulRaoof
Translators: Salim Abdullah Marjan
A nice discussion of some important points needed by those callling to Islam
Source: http://www.islamhouse.com/p/1243
A Book detailing the rulings concerning Hajj and Umrah.
Author: Mahmoud Reda Morad Abu Romaisah
Publisher: Islamic Propagation Office in Rabwah
Source: http://www.islamhouse.com/p/1391