Nothing will make you bigger and stronger than regular doses of squats and deadlifts. If you aren't incorporating these lifts on a weekly basis then I would question whether you are really strength training.
To make your strength training even more effective, consider using a method that is becoming more common now. Concentric only lifting. To do this, add extra drills that involve only the concentric portion of the lift. Meaning, pick the weight up and then drop it or lower it without fighting the weight. Think of Olympic lifters, they are able to handle much more volume (sets x reps x weight) than your average trainee because they drop the weight from the top. Why? Because it is less stressfull. So you get stronger without beating yourself up too much.
Now you still have to do plenty of lifting that involves the concentric and the eccentric (lowering) portion of the lift because that is the best way to build muscle. Think of this as an amazingly effective supplement to the base of your training. Instead of wasting time with minimally effective assistance lifts, spend more time doing the compound lifts, just remove the eccentric portion once you start getting tired.