I'd recommend the chapter on Marcionism in Heresies and How to Avoid Them (http://www.amazon.com/Heresies-How-Avoid-Them-Christians/dp/1598560131/ref=sr_1_1?ie=UTF8&s=books&qid=1242891133&sr=8-1). The whole book is based on a series of sermons in Peterhouse chapel Cambridge, each one on a different heresy, so it's intelligent but not quite academic. I really like the book for giving a quick overview of some of the most famous heresies. The author of the chapter on Marcionism is Angela Tilby who was the vice chancellor of a liberal high Anglican theological training college.