book recommendations for me?

I'd appreciate your help on this:

I'm putting together a list of books to recommend as an aspect of discipleship with Jesus (particularly for small-group studies to be read and discussed together).

I'm dividing the list into "200-level" and "300-level"-- where 200s are shorter & easier; and 300s are longer and/or heavier. I have a zillion books for the 200s, but am looking for more.

300s includes series/combos of books (e.g., four classics by C.S. Lewis) and some mid-level "equipping" curricula, but I'm looking for more individual books. The three examples I have at present: Willard's Divine Conspiracy, Chesterton's Orthodoxy, Piper's Desiring God.

Please list last name of author, book title, and a brief (5-10 word description). Thanks in advance!