I actually re-read it a couple months ago. This may sound surprising, but it influenced me most on the subject of immigration policy. Previously, I had been kind of iffy on the subject. I recognized that government barriers to the movement of labor were harmful in some ways, but I was worried that a policy of totally open borders would lead to unemployment, Americans losing their job, a decline in wages for working folks, and so forth. Then I realize that most of the same arguments used by Hazlitt in favor of free trade apply to immigration as well. I was already a free trader, so it only took a slight nudge by Hazlitt to put down the path to contemplating the possibility of free immigration.
I get something new out of Economics in One Lesson every time I read it.
Check my blog, if you're a loser
Economics in One Lesson is the book I point people towards usually.
I've just read Peter Schiff's new book and it is excellent. Very closely based on his father's story and drawings, but with a wider scope, more text, and the sequence of the story is more closely related to historical developments.
I may well start recommending Schiff's book as much as I recommend Hazlitt's.
Government Explained 2: The Special Piece of Paper
Law without Government