two for sure, the ring by dumbledore and the diary by harry.
The message said that R.A.B. intended to destroy that horcrux but who knows if he made it out of the cave at all, let alone still alive.. no one knows how long it has been since that message was there. i think that maybe this R.A.B. person poisoned the potion dumbledore drank and that's why he was weak.. i dont think voldemort wouldve been able to drink it to get to his horcrux unless there was another way.
Regulus Black may not have a middle that starts with A though. I don't think he was killed by the death eaters. i think that after bill's and fleur's wedding, harry will be looking for him and i think he will help harry reach his goal. I wonder if it's some one we know already or a new charater... may be it was a nick name.... ?