good fats are anything with high Monounsaturated and/or Polyunsaturated fats.. saturated and trans fats are the bad ones..
it all comes down to cholesterol. trans and saturated fats raise bad cholesterol which is LDL.
Monounsaturated raise good cholesterol which is HDL and lowers LDL
Polyunsaturated lowers all cholesterol which is ok but not the best

good foods:
nuts, extra virgin Olive oil, flax seed oil, all natural peanut butter (with the oil that is floating on top, mix that in and never pore it out.. that's good fat there), Omega 3, 6, 9s.., eggs, dairy, avocado

bad fats:
processed food, chocolate, candy, fat from meat (but a small amount is ok).

here's a site I like to use to find out some good food nutrition.
http://www.whfoods.com/foodstoc.php