As far as I've studied, high grade pharmaceutical fish oil (Omega-3 fatty acids) at a dose of 3 or more grams per day is pretty much the "super-supplement". Besides reducing over-all body inflammation, it's a huge anti-oxidant, fights cancer, fights brain disease, fights heart disease, high cholesterol, high blood pressure, improves glucose tolerance and fights diabetes...
the list goes on and on. If you are going to take anything besides a good general multivitamin, I'd recommend fish-oils.