The Affordable Care Act calls these "Essential Health Benefits" and every plan has them. They're required by law!
Outpatient services include any care received without being admitted to a hospital such as some minor surgeries, physical therapy, x-rays/MRI scans and counseling
Inpatient care is what insurance companies call any medical treatment that takes place in a hospital
Trips to the emergency room
Maternity and newborn care, care before and after your baby is born
Prescription drugs which includes any drug that requires a prescription, like Lipitor or your asthma medications
Laboratory services like blood tests, urinalysis and clinical genetic testing (though this doesn't mean that they'll cover your 23andMe purchase)
Mental health and substance use disorder services—this includes counseling and therapy
Rehabilitative and habilitative services and devices—various therapies and rehabilitation programs to help you recover from an injury or manage an ongoing (chronic) condition
Pediatric services includes not just medical care but also dental and vision care for your kids
Care for managing chronic diseases such as diabetes
Preventative services (these are free!) including basic vaccines, screenings and doctor visits. This last essential benefit is particularly important—preventative services are covered by your insurance at no cost to you! They cover a wide variety of health care needs and keep you healthy.