I am used to these:
"How's it going?" "Not bad, yourself?"
"What's up?" "Not much, you?"
"How are you?" "Pretty good, yourself?"
Someone asked me, "What's good?" the other day, and I said, "Not bad, yourself?" and then realized that that didn't make any sense, and I realized that I have never actually known how to properly respond to this greeting. I guess "Not much," makes sense but it seems very negative. But "Lots!" seems silly...
So what are you supposed to say?