Thanks to the Take Your Vitamin Z blog for this great list!

 

1&2 Peter: St Andrew’s Expositional Commentary
R.C. Sproul
$2.99

Isaiah (Crossway Classic Commentary)
John Calvin
$1.99

Excellence
Andreas J. Köstenberger
$1.99

Romans: Righteousness from Heaven
Kent Hughes
$2.99

FREE Absolutely Organize Your Family

 

FREE commentary on Ephesians (I know nothing about the author, sorry)