(I’ve read plenty of others in the past, but this is a 2016/17 reading list.)
- Pro Git – 2nd edition
This first came out in 2009 but was revised in 2014. If you don’t want to build the epub/mobi/PDF yourself, someone has uploaded a recent copy. - Ansible for Devops Jeff Geerling
- Programmers Guide to Drupal by Jennifer Hodgdon
Make sure you get the 2nd edition which covers Drupal 8. Parts of this are now out of date but it’s still extremely useful. Using Drupal 3rd edition
This was going to be an update to cover Drupal 8. Unfortunately it’s now been cancelled.