A staple in most lifting programs, the lateral raise is an extremely effective way to strengthen and tone your deltoids (shoulder muscles). They're somewhat easy to perform, and I am almost certain you already know how to do them.
Just in case you don't, a quick how-to:
Grab a lighter set of dumbbells, one in each hand. Relax your shoulders and place your arms at your side. Legs should be hip-width apart. Simply lift the dumbbells out to the side of your body until your arms are parallel to the floor (you'll look like a "T"), then relax back to start. Reps are up to you, arms can be straight or bent at 90 degrees.
Easy, right? Almost too easy, I think.
Try it this way: Sit on the floor or a bench, maybe even a BOSU ball, and lift your feet a few inches off the floor. Use your abdominal muscles to balance, and keep your back relatively straight. Lift as instructed above without letting your feet touch the floor.
Not only will you get a great shoulder workout, engaging your abdominal muscles and lifting your feet throughout will add a core bonus. And if you're anything like me, you're always looking for that added core bonus.
Try it, I promise you'll like it. Or at the very least, develop a love/hate relationship with it.