Here are some external opportunities, organized alphabetically by specialty area/disease category:

Anesthesiology
Cardiology
Community Health, Rural Health, Global Health, and Health Disparities
Dermatology
Emergency, Trauma, and Wilderness Medicine
Endocrinology
Gastroenterology
Geriatrics
Health Policy
Hematology
Immunology
Infectious Disease
Medical Ethics and Medical Humanities
Mental Health, Psychiatry, and Addiction
Nephrology and Urology
Neurology
Nutrition
Oncology
Ophthalmology
Orthopedics/Musculoskeletal
Pediatrics
Pulmonology
Radiology
Reproductive
Surgery
General/Miscellaneous

You can also find some other short-term opportunities (like fellowships, which are great for summer) at the UNC SOM Office for Medical Student Research website.