A Brief History of Theology, by Derek Johnston.
This is an excellent 300-page survey of 2000 years of Christian theooogy. In sixteen chapters, Johnston covers the early church (Sts. Paul & Augustine), the middle ages (Aquinas), the reformation (Luther, Ignatius, Calvin) and the last century (Barth, Rahner, Brueggermann). Each of these theologians are analyzed in their social and cultural settings, and their life and teachings are appraised in these contexts.
The book is not always an easy read -- because the ideas of these theologians do not always lend themselves to an easy read. But it is indeed a worthwhile overview of the broad theological landscape.