Here's a wonderful exercise to bust up your arms, back, chest and core. Alas, I forget the name of the exercise, so hopefully someone else here will recognise the description and be able to label it.
Set up your two dumbells on the ground, about shoulder-width apart. Get in a push up position with your hands around the dumbells, and lower yourself down to the bottom position of a push up. Push yourself back up, and when you get to the top, row one arm at a time up to your side and then back down again, keeping the grounded arm straight and the chest horizontal (lift the dumbell with your shoulder and arm, don't rotate your torso to lift the weight). Once you have completed a push up and a row on each side, that's your first rep.