I dove in the Cook Islands in January 2002, at Aitutaki atoll. Although I would highly recommend going to Aitutaki (the most beautiful atoll I've seen to date) for the largely-intact culture and stunning vistas, the seaward reefs and ecosystem weren't that impressive. Coral is drab brown or grey, as are many of the fish, explained in large part by a coral die-off last decade during El Nino warm spells. I don't remember seeing too many soft corals. Lots of fishing pressure for reef fish (tackle and spear) except for some legally protected areas within the extensive lagoon and inward reef. But the blue sea trolling there was impressive. Lots of yellowfin, wahoo, skipjack and baitfish b/c not too many international fishing fleets can bypass the local coast guard. Snorkeling in the protected areas, however, was among the best I've seen anywhere, including Belize and Hawaii. Flights to the Cooks (you have to enter through Rarotonga) are a bit pricey, around $1000 from California. Air New Zealand is the major carrier, and I believe at one point they had a flight from Honolulu, around a six hour flight. Nine hours from California, with departures from LAX and recently SFO.
I've attached some photos (copyrighted, sorry to add) from Aitutaki atoll: outrigger in the fringing lagoon, first view of the atoll islands (motus) from the plane, traditional dancers (the best in the South Pacific, IMO), a beach scene, and a spinner dolphin. Aside from the diving, Aitutaki was my dream vacation.
