[jstx1]

The Mathematics of Poker, by Chen & Ankenman - this one doesn't age because it's really fundamental if you want to understand things from the ground up. But it won't seem that practical at first.

Applications of No-Limit Hold 'em, by Matthew Janda - this one goes into specifics about how to think on each street, how to build a good strategy etc. Some of the details will be different from the latest theory because the book was released in 2013 but it's still a very solid read if you want to level up.