The free book this month from Ligonier Ministries is
Surprised by Suffering by R. C. Sproul. It's available at
Amazon or as a DRM-free epub at Ligonier's
online store.
What looks like some old-fashioned fire and brimstone,
They Thought They Had More Time: I Saw the Day of the Lord by David Jones, is free from Destiny Image.
B&N Amazon
If you're a fan of Warren Wiersbe's Bible studies,
The Wiersbe Bible Study Series: Genesis 1–11 is free.
Publisher page
The other David C. Cook freebie,
Discover the Mystery of Faith by Glenn Packiam has been free before, but maybe it's new to you.
Publisher page
If you haven't checked lately, the Baker Publishing Group has almost fifty free books. Most of them have been free for a few months, but there are a few new ones in the list.
Baker Publishing at B&N sorted by price
Those should also be free at Amazon, but they're split into the different imprints (Revell, Bethany House, Baker...) so there isn't one link that will list all of them.