I echo others mentioning Thich Nat Hanh (RIP). I've found his work really helpful, esp a book called 'Reconciliation - Healing your inner child' - which might sound a bit ctingeworthy but it's actually brilliant.
There are a great number of books by Thich Nhat Hanh. I've read several. Once you've read a handful, you'll find there's stories and metaphors he returns to again and again. Which is fair enough: his message is pretty simple (although also profound), and that's: the present moment is the only one you can actually live, and you can access it more fully by returning to awareness of your breath. Even his coinage
Interbeing is a concept that is intended to work in service of mindfulness of the breath and the present moment.
Thay (as his admirers call him, pronounced "tie" - it's an informal Vietnamese form of address meaning "teacher", and one you can apply typically to any monk or person imparting wisdom, but which has come to be TNH's affectionate nickname), was capable of intellectualising the Buddhist canon. He spoke several languages, including Chinese, English and French, as well as the literary scriptural languages of Pali and Sanskrit, and has done comparative translations of sutras found in the "Northern Transmission" (ie, preserved in Chinese or Tibetan, broadly Mahayana Buddhism), and the "Southern Transmission" (ie preserved in Pali, broadly Theravada). He keeps these accessible, but after ploughing through several pages of The Four Jhanas, The Five Skandhas, The Eighteen Something Elses, you can be forgiven for glazing over and wishing for another "breathing in, I know I am breathing in". (Which will come, don't worry about that). But there are other books that are far less theoretical, and easier on the casual reader.
Reconciliation, although very useful (I agree with
han - it's a gem) is one of those.
My recommendations are.
For the casual reader
Peace is Every Step (the best introduction to his thinking. If you have this, you don't need The Miracle of Mindfulness, which actually I'm not as fond of).
Buddhist Theory
The Other Shore (a translation and commentary on the Heart Sutra, and a very useful book. One of my favourites. Very accessible, and suitable for someone who has read, say, Peace Is Every Step.);
Zen Keys (an early book, and a general introduction to Zen);
Awakening of the Heart (a much larger compendium of translations and commentaries on sutras, much more of a commitment).
If you want a more technical book, the
Heart of the Buddha's Teaching is good, but it does drift off into 18 This, and 14 That, and so on.
There's a few things about his work that as a secular practitioner I find very useful. He never makes any supernatural claims. (He does sometimes talk about "the kingdom of god", but he very clearly uses it as a synonym for the Universe, or "the Pure Land of the Buddha", which he says is
only available in the present moment, so he just means the benefits of mindfulness). Everything is very grounded in what is useful in the present moment. On reincarnation, he talks about genes, about the impression you make on others and on the world, the atoms that make up your body being reused. He even talks of energy-momentum conservation: the heat of your body returns to the universe when you die. It doesn't disappear. And so on. He talks of our genetic inheritance going back through our parents and grandparents, even beyond the human species, into non human ancestors, right back to single celled organisms. The conception of reincarnation he offers is compatible with science and with social theory. Nothing supernatural. In one video he is asked by an audience member "what happens when you die?". He replies "what happens when you live?". That can be taken a number of ways. The technical: "Do we really understand what life is?" Or the more instructional: "be alive in the present moment. Don't live in the future".
The next thing that's useful to the secular practitioner is that because he's from Vietnam, which has both the Theravada and the Zen (Mahayana) traditions in its culture and history, he presents a synthesis of those traditions. He takes what is useful in both traditions. He makes a comparison to get at what he believes is the deep core of what the Buddha's teaching was about and, in essence, what it was
for.
Finally, he is interested in "engaged Buddhism". His personal experiences in Vietnam, of both "The French War" and "The American War", meant he is steeped in practicality. His order were out in villages tending the injured and dying, repairing buildings, rehoming orphans. He doesn't want us disappearing into a mountain hermitage and staring at a wall for years in order to Attain Enlightenment. He wants us to take care of our psychological well-being so that we can better cope with the demands of activism. He is engaged with social justice, environmental justice, discrimination, and so on. He uses the analogy of an oxygen mask in an aeroplane: you attach your own mask so that you are able to care for others.
I think his stuff has something to offer us.
I just finished reading "When Things Fall Apart" by Pema Chodron, which has really clarified a lot of things. I am a mess right now 
