I've recently read Debt is Slavery, Your Money or Your Life, and Early Retirement Extreme. I thought they worked really well in that order.
Debt is Slavery is the short, but sweet, wake up call which identifies debt for what it really is. It provides a taste without wasting any words.
Your Money or Your Life lays things out in 9 steps. There are groups that meet just about this book. YMOYL covers setting up a budget, rethinking satisfaction, monitoring progress, and reaching FI - the nuts and bolts.
Early Retirement Extreme takes YMOYL to a whole new level. It assumes you're already on board with the whole live cheaply idea, and goes into the details of what that will mean. At the same time, it tries to teach principals instead of concrete examples. This both ensures that it doesn't get dated as well as teaching you the steps necessary to be successful.
Of those three, I felt YMOYL was the most valuable, and the one I've shared with non-mustachian friends. All three are motivating.
A few months ago I also read Consumer Detox. I was disappointed and wouldn't recommend it. It never gets into practical, motivational discussion about what to do about consumerism - it just points it out in one obvious example after another. It's an easy book to get through, but not worth it, in my opinion. It's written from a Christian perspective which might not align with others belief systems or interests. Overall, it's just not as good as the other three.
As soon as my hold is fulfilled, I plan on reading the Intelligent Asset Allocator. I'm in the 'stache building phase and need to develop and refine an investment philosophy.