There are several federal programs that range from the Armed Forces Health Professions Scholarship Program to the National Health Service Corp programs. These require a commitment after residency.
Some schools give out some scholarships. I received two small scholarships from my school. Most financial aid departments will automatically apply to these scholarships on your behalf. Check with them to see if they do that.
A couple of the medical organizations have scholarships (e.g., Southern Medical Association). The SMA scholarship is open to third year medical students only.
The last option is to do what I did. Contact a hospital or the Board of Commissioners where you want to practice and ask them if they would give you a scholarship or sponsor you if you come back there to practice. I received a $10,000 scholarship without a firm commitment from a local hospital for whom I used to work. The catch? Nothing. The award acceptance states that I will consider practicing there, but it does not state that I must practice there. A good deal of money for no commitment (although I actually do plan to practice there).
Good luck!