The "bus driver" exercise is where you hold a plate at arms length in front of you and rotate slowly. It's a hugely underrated movement. It's an excellent way to finish the shoulder workout and make the joint more resilient to injuries.
Start with a 10 or a 25 and work your way up to 45 pounds.
Are squats and deadlifts all you need to work your core? Is it "bad" to do static stretches before weight training? Answers to these questions and more.
They're one of the most difficult muscle groups to develop, but the cure to your underdeveloped hamstrings might lie in the answer to this question: "Which way do you point your toes during a leg curl?"