Most everybody knows the saying I've alluded to in my title. I believe the saying to be inherently true, and not just in terms of repeating your history CLASS, but repeating the negative lessons of history itself.
It was Chesterton, I think, who said something like, "The wit of man in insufficient to invent a new heresy." I'm not positive my wording is exact, or even that someone other than G. K. said it originally, but either way, I love the saying because it seems to incorporate truth in a very consistent manner.
If we look around at all the various weird religions, pseudo-Christian cults, and spiritualities that are around today, it seems all of them (that I've found) have a strong parallel, if not are an exact duplication, of a heresy from the first five (or so) centuries of the church.
So, with all that in mind, I constantly push my Sunday School class along with anyone else who will listen to be well-versed in the history of the Christian Church, especially where it concerns aberrant teachings. Tim Challies has started what promises to be a very useful series on the seven great church councils on his blog. The first post can be found here. I sincerely hope many will read these posts, and they will be helpful in the edification of the church.
Obviously, we as Christians should have a good command of the Bible, and the Bible should be the primary locus of our study. But one of the ways of correctly understanding the Bible is to know and understand way it has been misinterpreted in history. These posts will give a good non-seminary-level overview of these misinterpretations.
May I suggest a few good books that I've used on this topic as well (each title is a link to the book on Amazon.com):
1. Heresies, by H. Brown
2. Heresy, by A. McGrath
3. Turning Points (first four chapters) by M. Noll
4. Historical Theology, by G. Bromiley
5. Historical Theology, by G. Allison
6. Historical Theology, by A. McGrath