The Silo series by Hugh Howey starts out with Wool. I first read Wool (the Omnibus edition) because a friend at college had talked it up. I borrowed his copy and was completely engrossed. I loved it. It tells the tale of a group of people living in a silo underground. The outside world is uninhabitable and they are the last of mankind. The top floor of the silo has a window to the outside, so the inhabitants can see what the outside world looks like.
I'd highly recommend the book. I first read it about three years ago and just started to re-read it.
There are two more great books in the series, Shift (Book 2), and Dust (Book 3). Shift is a prequel and gives you a look at how the world came to be in Wool. And Dust finishes up the series. I'd recommend at least starting Wool to see what you think.
What have you been reading lately?