If you're looking at shore diving, which is fabulous in Kona for ease and quality, here are just a handful out of dozens:
Puako - go early in the day, watch the conditions
Keahole Pt - great for big schools of fish, occasional pelagics
Old Airport - best for poking around the underwater cliffs and 'caves' if that's what you like
Kahaluu Beach Park/Fish Bowl - the shallow fish bowl is fun for the abundant and tame fish life, but outside the breakwater to the south, as far down as the far side of the Keauhou Outrigger (maybe farther!) has good lava canyons; this can be a long swim
Ke'e - good coral here, and visibility
Place of Refuge - fabulous coral out to the south, great schools of fish life at the point, good coral and exploring to the north; Dolphins occassionally
Kealakekua - you have to kayak out or take a boat but the fish life is (usually) unparalleled over anywhere else. Good for photos because the fish aren't as spooked. Snorkeling almost as good as diving. Dolphins likely
Anyplace you can get to the water from the Airport south to South Point, literally. North of the airport there are some silty bays to avoid but elsewhere great diving.
If you're on the southeast side below Hilo, check out the extensive tidepools at Kapoho for incredible snorkeling and rare corals. Conditions can be rough.
I too highly recommend the awesome manta dives off the airport - last I heard the ones down at the newly renovated Sheraton, the old spot, hadn't been too good, though you can go there and see them from the hotel walkways.
Good to hear about the black water dives - I was skeptical when I heard them described.