Christianity and its Competitors: The new faces of old heresy, by James McGoldrick (Christian Focus)
Kingdom of the Cults (6th ed.), by Walter Martin (Bethany House)
God among Sages: Why Jesus Is Not Just Another Religious Leader, by Kenneth Samples (Baker Books).
World Religions and Cults: Counterfeits of Christianity (Vol. 1), eds. Bodie Hodge & Roger Patterson (Master Books).
World Religions and Cults: Moralistic, Mythical and Mysticism Religions (Vol. 2), eds. Bodie Hodge & Roger Patterson (Master Books).
World Religions and Cults: Atheistic and Humanistic Religions (Vol. 3), eds. Bodie Hodge & Roger Patterson (Master Books).
The Evangelical Dictionary of World Religions, Gen. Ed. H. Wayne House (Baker).
The Challenge of the Cults and New Religions, by Ron Rhodes (Zondervan).
Encyclopedic Dictionary of Cults, Sects, and World Religions (Rev. and updated), Eds. Larry Nichols, et. al. (Zondervan).
Index of Cults and Religions, by Watchman Fellowship.
Watchman Fellowship Profiles, various authors.
A page of resources on Mormonism here.
A page of resources on the Jehovah’s Witnesses here
A page of resources on the Baha’i Faith here