Prefatory qualifications: most of my reading in 2010 was rather narrow-minded, so if you're looking for a broader list of books I'd commend Christopher Benson's list to you.
Additionally, I approached the list through a pretty narrow lens: these are books that I think will be particularly helpful to evangelicals.
The Deep Things of God. My initial thoughts are here, but I have a more thorough review forthcoming in Christianity Today. Needless to say, I'm a fan. Sanders' book is a critical contribution to both those who wish to understand what it means to be an 'evangelical' and those who wish to understand the nature of God. Check out the final paragraph of this review if you don't believe me.
Defending Constantine. Massively important for challenging the commonly accepted narrative of the saint (according to the Eastern Orthodox, anyway) whose name has been reduced to an insult. Highly, highly recommended.
For the Beauty of the Church. I interviewed David on this for my podcast, but technical difficulties (alas) made it all but unusable. The book is an important and incredibly useful guide for churches, pastors, and laymen who are interested in how the church and the arts go together. There's a diversity of perspectives in the book, which makes it even more fun.
To Change the World. Spilled plenty of words on this one, so I won't say anything other than that it serves as a helpful resource for thinking through how evangelicals relate to politics and culture.
Washed and Waiting: Reflections on Christian Faithfulness and Homosexuality. I have a full review of this coming in the new year, but I'll say this now: If I had to pick any one book from this list for evangelicals to read, it would be a tossup between Deep Things and this one.
Living in Two Kingdoms: I haven't written as much about this one, but it's a helpful challenge to the Kuyperian account of common grace that has become so popular. It's not for everyone--those wary of the regulative principle, for instance, can skip those sections--but it's an important book nonetheless.
Generation Ex-Christians: with all the talk of those young Christians who are leaving the church, no one had done a survey of the complex set of motivations and factors that cause people to leave until Drew Dyck took on the case. It's not a work of sociology, and it's not quite ethnography either. Dyck's examination, though, of the six different reasons why young people quit identifying as Christians is, in my experience, extraordinarily accurate.
Against all Gods: Reynolds and Johnson are, as we've come to expect from both, insightful and interesting. It's not a head-on critique of the "new Atheists," but it's an enjoyable read nonetheless. There's a helpful review of the book here.
The Art of Dying. I was happy to see someone take on this issue, and Moll does a great job with it. Evangelical practices around death and dying have been a concern of mine for some time, and Moll's book does nearly everything I hoped it would. Highly commended.
Homosexuality and the Christian: Part of the problem of the conversation about the relationship between homosexuality and Christianity is that there is so much confusion over what the phenomenon is that we're trying to understand in light of Scripture. Yarhouse cuts through the ambiguities to carefully distinguish between sexual identity, orientation, and attraction and relating each to the truth of the Gospel. Yet this is a practically minded book that is very helpful.
Your Church is Too Small. This is a manifesto for a missionally minded evangelicalism that stresses church unity. Armstrong has been around a long time and knows just about everyone, so he writes with a sense of passion and fervor that few are able to muster. I'm not normally in the prediction making business, but I suspect we'll hear a lot more on unity and ecumenicism the next five years, as it sounds like N.T. Wright is going to drop in on the subject soon. Armstrong's book is a helpful dialog partner to warm you up for the conversation that's coming.
Ecumenical Babel: Want to see the dangers of how the modern ecumenical movement has played out? Jordan Ballor's tour and critique of some of the central ecumenical statements in the past fifty years highlights the influence of liberation theology and the adoption of neo-Marxist economic policies. It is a helpful book to read in conjunction with Armstrong's book, as it serves as a caution as what ecumenicism should not be.