Michael
PNG has a multitude of plane wrecks strewn all over the islands. Kavieng has the quite cool Taisho Maru which has a minisub (which apparently still has a video rig in there) and of course plenty of Judy and Kate aircraft. There is a blackjack (B25) as well and a newer Korean boat which is boring if there weren't any dogtooth tuna flying around.
Rabaul lost quite a few wrecks during the eruption but the biplane and tankers are still there.
One place that is underrated for plane wrecks is Port Moresby. I saw a P47 thunderbolt, Judy, P38 Lightning and a few other planes. You have to contact John at the Dive Center in Port Moresby. Those wrecks are out in the muck and getting the right viz and tide is important.
The Kokoda trail is about to be history(well 400m of it anyhow) due to mining and there were some security issues going through it a few years back. I've done it without incident.
For Indonesia, the wrecks are spread out and quite deep. PM me for the contact for the guy who specializes in wreck diving in Indo ( he even has his own DC chamber onboard).
The best accessible wrecks around Papua Barat are situated Manokawari bay, and not in Raja Empat. Off the top of my head, I remember 2 wrecks, the Shinwa Maru and the Cross Wreck (which reminds me to find out what the japanese name of the boat is). 'Mad' Max Ammer from Papua diving conducts occasional trips there and there is a liveaboard that covers this area from Biak.
It also ghas great ripping drift dives with big pelagics.
I spent quite a bit of time in Kavieng and the pelagic dives aren't all that good all the time. It's very dependent on the moon phase and time of year. You can get some good stuff occasionally but the pelagic paradise of Kavieng is to be taken in context to the rest of PNG. Reef hooks are not an optional accessory in many of the channels too.