Here are a couple theories I've developed about since reading the 5th Harry Potter book. Tell me what you think of them!
1) I know that the "Mark Evans" (the 10 year old that was beaten up by Dudley) theory has been mentioned alot in a couple websites. Some people believe that this could be a somehow distant relative to Harry (because Evans was Harry's mom's madien name), but this isn't possible, because in the first HP book, Dumbledore says 'I've come ot take Harry to his aunt and uncle. They're the only family he has left now."
2) I haven't really heard this one yet, but it seems that the portraits had a lot more importance in Book 5 than the other books. What with the old headmasters running around doing "errands" and spreading information. So I thought it could be possible that Sirius had his own portrait hanging around somewhere in the Black Manor. If this were true (though Black's mother hated him so much she might have burnt down any portrait that had Sirius in it) then maybe Harry would find a hidden room and be shocked to see Sirius or hear his voice. I'm also just too stubborn to believe that Harry will NEVER see Sirius again, especially since he was so vital to getting Harry important information, and would go to any means to help him.
Thanks, and tell me your ideas based on these!