While the good people in this section will give you breeds, I just want to add that a great deal of what makes a dog calm or aggressive is the dogs individual temperament and personality, as well as training.
I have a Germans Shepherd, my good friend owns my dogs brother. Two male dogs, both from the same litter, but my dog is laid back and calm, his brother is hyper and a wild child most of the time. Some of the difference comes from temperament, some from training.
If you get a puppy, here is a tip. Walk up to the pen of puppy's, and pick them up one at a time. put your hand under their belly, lift them up about a foot or two off the ground. If a puppy struggles right away to get down, it has a aggressive temperament, and needs a skilled, experienced owner. If the puppy just hangs there, and never struggles, that puppy is too passive, and will likely grow up to be a fearful dog. Fearful dogs become fear biters. They too need a skilled trainer. You want the one that will hang for a few moments before struggling to get down. Usually that is a indication of a natural calm, even temperament.
This is not the only thing you should look for, but it is one of the easy test to do.
Best of luck