In the 5x5 and Starting Strength genre which offers a foundation and up style of conveying training theory (which most people who are using this site will find most useful) the following are currently or will be available shortly. Starting Strength covers the lifts, basic info and introductory programming while Practical Periodization will cover how, why, and when training is altered through time as the lifter progresses and gains experience. More info on these first 3 books here.
The following are some of the best books on training theory available. Most are available either through EliteFTS or Sportivny Press Weightlifting Texts accessed through the Dynamic Eleiko site and then products:
An of course dealing with training the body requires an understanding of the body and its systems. I basically just went with Mike Hartman's recommendation (link is dead) on several of these. For most people, just go find a deal on something somewhere. Enoka's book has been particularly helpful in understanding many topics related to exercise - there's probably not a better source out there currently and it is highly recommended by almost everyone.
