I found some interesting resources on Habakkuk after following up on a quote found in Ryken’s Bible Handbook:

God doesn’t always change the circumstances, but He can change us to meet the circumstances. That’s what it means to live by faith.

–Warren Wiersbe, Conclusion to his outline of Chapter 3

You can find these outlines in HTML format at these links:
Habakkuk 1-2:4
Habakkuk 2:5-3:19

The outline is very colorful–literally. Much of Habakkuk is applied to our present day world and New Testament references are noted. There is quite a bit about Reformed theology throughout.

Another resource I happened to find is by Dr. Thomas L. Constable of Dallas Theological Seminary.
Notes on Habakkuk – 2010 Edition

I like this quote he includes which part of why Habakkuk is so interesting.

Habakkuk is a unique book. Unlike other prophets who declared God’s message to people this prophet dialogued with God about people. Most Old Testament prophets proclaimed divine judgment. Habakkuk pleaded for divine judgment. In contrast with the typical indictment, this little book records an intriguing interchange between a perplexed prophet and his Maker.

–Ronald J. Blue, “Habakkuk.” In The Bible Knowledge Commentary: Old Testament p. 1505

And of course there is John Hobbin’s blog Ancient Hebrew Poetry which starts out here:
The Book of Habakkuk: An Introduction
I think you can find the rest via Google.