I've had The Mormon Question on the sidebar for a very long time. I'm just about finished with it now (I didn't read it for nearly a month because of traveling and moving) and it is fascinating. I'll have a better review of it soon, but the thing I've enjoyed most is the way this book combines the religious and secular histories I'm so interested in. This is not something you'll get in any American history textbook even though polygamy did have a major effect on late 19th-century America.
I'll be moving on to Zion in the Courts next. It's nice that Nate Oman reviewed both these books a long time ago.