You have a few options: 1. Butter is a classic, of course, and ghee is excellent too. 2. I really like cooking eggs in duck fat. I get it at Whole Foods. It's delightfully flavorful. When using duck fat you never have to worry about your eggs ending up bland. 3. Another high-flavor option is to cook them in the bacon fat leftover after baking bacon in the oven. It's really good! 4. And finally, Cooking eggs in olive oil is nontraditional but surprisingly good too.