For nice and cute things, women would say 어머, 어머나. Men say 야아, 와아, and similar interjections. For something gross or bad, I don't know of a particular thing they say. They would just say 아, 어, or 이, and the like. It is the drawn out and changing tone expresses the feeling, not the word itself. So in many cases there is no particular word but just 아, 어, 에, etc with a particular intonation.