ACT for Depression is the first book on ACT for depression. The author has published two randomized trials providing support for the use of ACT for depression with ACT performing equivalently to or better than cognitive therapy (the current gold standard for depression).

Acceptance And Commitment Therapy For Chronic Pain focuses on the application of ACT to chronic pain specfically and also includes some information working with professionals using ACT. This book focuses heavily on values interventions and so can be a good resource for those wanting to learn more about using values in ACT.

Act on Life Not on Anger: The New Acceptance & Commitment Therapy Guide to Problem Anger is another self-help book on ACT. I haven't read it yet, but have had a couple clients say it was quite helpful. The authors are experienced ACT therapists and authors.

Living Beyond Your Pain: Using Acceptance & Commitment Therapy to Ease Chronic Pain is a self-help book on ACT focused on chronic pain. This book is based on pain interventions that have been shown to be effective in at least three studies, so there is some evidence that this might be helpful.