The volume of profitable expositions and guides to the Heidelberg Catechism is quite large. As far as modern works, I would suggest:

G.I. Williamson, The Heidelberg Catechism
J. Van Bruggen, Annotations to the Heidelberg Catechism
Joel Beeke, Heidelberg Catechism Sermons
Lyle D. Bierma, An Introduction to the Heidelberg Catechism
G.H. Kersten, The Heidelberg Catechism in Fifty-Two Sermons
G. Van Reenen, The Heidelberg Catechism

I have provided links to online editions of Kersten's work and other valuable older studies of the HC and the Compendium here.

__________________
Andrew Myers
Husband of Jessica, Father of Jackson, Katie and Samuel
Member, Presbyterian Reformed Church of Northern Virginia
Warrenton, VA USA
Editor, The Matthew Poole Project

"Let your Morning Thoughts, and your last Evening Thoughts, be what shall become of you to all Eternity." -- Matthew Poole