So here's my list. These aren't only "Lenten books" but rather books that Curt and I think help us want to be holy... and that's what Lent is all about!
So here they are, in no particular order:
Called to Holiness by Ralph Martin
Prayer and Temperament: Different Prayer Forms for Different Personality Types by Chester Michael and Marie Norrisy
The Seven Storey Mountain by Thomas Merton
No Man is an Island by Thomas Merton
Love is Stronger than Death by Peter Kreeft
The Better Part: A Christ-Centered Resource for Personal Prayer by John Bartunek
Characters of the Passion by Fulton Sheen
The Great Divorce by C.S. Lewis
Everything You Ever Wanted to Know About Heaven by Peter Kreeft
Journey Toward Easter by Cardinal Joseph Ratzinger/Pope Benedict XVI
Collected Words of St. John of the Cross
If Your Mind Wanders at Mass by Thomas Howard
In Conversation with God Vol. 2 - Lent and Eastertide by Francis Fernandez
If you have any suggestions of your own, please include them in comments!!