Hey there,
There are all types of "fellowships" in family medicine, fellowships being defined as additional training beyond residency.
Not all fellowships lead to add'l degrees or certification.
The "recognized" fellowships (those in which you can take a test and get a 'Certificate of Additional Qualifications' (CAQ) are
1. sports medicine
2. geriatrics, and coming soon
3. adolescent medicine
There are also fellowships available in Obstetrics/Women's Health, Faculty Development (either teaching, research or patient care), Emergency Medicine (though i think these are disappearing) and loads of others...
check out
http://www.aafp.org/fellowships/
hth
-ed