I looked over the FAQ and didn't see many books on the Old West or American Frontier, but would love to read something about those subjects if any one can offer some good books. I don't know much about those subjects at present, so something fairly introductory would be fine, but I'm also interested in something that might be a bit more specialised.
I'm in the process of updating that section! And you've inspired me to hurry up! My personal recommendation would be The Legacy of Conquest by Patricia Limerick. It's one of the first extensive works dealing with a "new" vision of the West, which seeks to understand the American West in its broader economic, federal and global context. Limerick does a good job of addressing the flaws in a romantic vision of the frontier and Turnerian-based theories. If there's anything specific you are interested in I would be happy to make some recommendations.
I second the recommendation of Patricia Limerick. I would also suggest Susan Lee Johnson's Roaring Camp if you are interested in California's Gold Rush.