Dumbbells are essential for moves like bicep curls, shoulder presses, and more. Add weights to squats and deadlifts to build strength. These Yes4All Adjustable Dumbbells ($45) weigh 40 pounds total and come with four five-pound and four three-pound plates, and you can take off plates as needed to adjust the weight of each dumbbell. Check out this arm and ab dumbbell workout to start.