On Oahu, I'd suggest Kaimana Divers and/or Hawaiian Diving Adventures if you're around Honolulu/Waikiki or the West side. Regardless of who you wind up booking with, a call to Gabe at Kaimana to talk about what you want to do and what's available around the island vis-a-vis wreck and shore dives...would be a good investment of your time.
Aaron's is an awesome shop, but is located in Kailua on the windward side near Kaneohe, and tends to dive the Hawaii Kai area I think (I may well be wrong) which I don't find as interesting unless you're doing something they'd consider risky and subject to conditions, like drifting Sea Cave or Spitting Caves. Which is not to say they're not awesome--I really like the staff there, and they clearly know their stuff.
If you're on the North shore, I've heard good things about Deep Ecology in Haliewa or however it's spelled, but I've no personal experience with them.