Chopped fresh herbs like parsley, chives, basil, or cilantro. Add them while the eggs are cooking.
You can also addsalsaorpico de gallo. You can add them while the eggs are cooking or spoon them over the top when you serve them.
Or add some of your favorite hot sauce to give them a spicy kick.
I usually go with shredded cheddar cheese, but you can use grated Parmesan, shredded Monterey jack or pepper jack cheese. Crumbled feta or goat cheese is great, too!