> Starting Strength - because this time I actually started lifting instead of just reading it :)
For me it's High-Intensity Training the Mike Mentzer Way. Frankly I don't care about strength, and am focusing instead on bodybuilding.
I used to spend a lot of hours in the gym not really knowing what I'm doing (no plan, no goals). After this book I now have a good plan and clear, predictable goals.
Which 1970s bodybuilder isn't? Besides, he perfected his programme on his clients, not himself. Anyway, it works perfectly well for me, I couldn't be more satisfied with my progress and thus have no reason to change my plan. I'm glad SS works for you.
Conversely, if you're done with losing fat and wish to add some muscle I would recommend the High Intensity Training technique, described in e.g. the book High-Intensity Training the Mike Mentzer Way. The basic idea is to train once or twice a week for around 30 minutes, send as big a signal as possible to your body that your muscles are inadequate, and then recover until the next session.
Not to be a downer, but I have spent a lot of time in powerlifting/bodybuilding circles, and I've never met anyone with an advanced physique that told me that type of training worked for them.
I've also tried training that way, and didn't see good results.