Valiant For Truth, the blog of Westminster Seminary California have produced a list of books which are based upon, or deal with the Heidelberg Catechism as part of their Building The Minister’s Library series of posts.
It’s a helpful reference.
Becoming conversant with the Heidelberg Catechism has been a helpful complement to its Westminster counterparts.
I’ve got The Good News We Almost Forgot by Kevin DeYoung, which is a primer/overview of the catechism.
Some of the other books look interesting.