I recently read "Christus Victor" by Gustaf Aulen

I admit, this is not an easy read.  It's quite deep, and I probably understood only about half of it.  But it gave a good history of the three different views of the atonement: the Eastern church fathers, the western view, and the modern liberal view.  It stretched my thinking, and I learned something, though personally I prefer books that are easier to understand.

You can see all the books I've read so far (starting in 2011) here.