Probably the most glaring error of the JW’s is that they believe that the Lord Jesus Christ is a god not the God. They have a works salvation scheme. Have both doctrinal and some sociological characteristics of a cult. I have put these links in order of priority.
Cold-case Christianity with J. Warner Wallace: “A Brief Overview of the Jehovah’s Witness Worldview”
Christian Research and Apologetics Ministry—Links to several resources about Jehovah’s Witnesses
ReligionFacts: “Jehovah's Witnesses Beliefs”—A non-evangelical summary of their beliefs.
ChristianAnwers.net—“How do Jehovah’s Witnesses’ teachings about Christ compare with Scriptures?”
Defense of Christ’s deity geared toward JW’s
Bible.org—This page has several good articles about Jehovah’s Witnesses.