Majoring in biology is a common choice for premed students because of the sheer amount of information that will overlap between college and medical school. Since biology deals mainly with the functions of the human body, most of the classes you will take in the course of this major will be applicable and useful for a life as a doctor. Majoring in biology will also fulfill the majority, if not all, of the prerequisites you will need to get into medical school, so you will not be burdened by additional coursework outside of your major.
Like biology, chemistry is a common choice for premed students because it also fulfills a lot of the prerequisites for medical school. The information that you will learn in the chemistry major, as well as the labs that accompany the classes, is generally knowledge that is helpful for a doctor to know.
If you are interested in subjects other than science and you can handle the course load of one major while fulfilling requirements in another, you might consider majoring in something other than science. Because most students applying to medical school have majored in either biology, chemistry or something similar, your application will stand out if you majored in a totally different subject. The possibilities are endless: you can major in religion, history, English, journalism or anything else you like as long as you have fulfilled all of the necessary prerequisites for medical school. In a standard liberal arts college, you will probably have taken the basics already, but you should check with the medical schools that you wish to apply at to make sure that there is nothing else you should take. As long as you have earned good grades in both your major and the subjects relating to medical school, your status as a nonscience major can be a definite asset.