Below follow my observations concerning all three covers. If that counts as a spoiler for you guys, please don't read any further.
First of all, here's the link to all three covers:
http://www.mugglenet.com/app/news/show/751 I'll take them one by one.
US Cover: Wow o.o Okay, so the two people in the forefront are obviously Harry and Voldy. But neither is holding wands. I guess it would be kinda pointless for the two of them to fight with wands, seeing as Priori Incantatem can get a bit inconvenient. Though that would mean Harry can do wandless magic by that point. Come to think of it, he already has done a bit (remember in OotP where he summons his wand to his hand during the Dementor attack?) but being cool about being wandless would mean that he now kicks ass even without a wand. And as talented as Harry is, he's nowhere near Voldy's level even WITH a wand. Could it be that he feels confident enough not to be hexed for a specific reason? Hmmmm...
I mean look, they're not even fighting. They're both staring at something and look almost as if they're reaching out for it. Also, notice how there's CURTAINS? O.o What up with that? My first thought was that they're beyond the veil or summat, but the veil's supposed to be black. Then again, perhaps it only looks black from the outside?
Of course, entering the veil would mean that both V and Harry are dead at that particular point in the book o.o At least from what we know so far. Also, there's a friggin' AUDIENCE there o.o;;; That would tie well with what I said before about the veil. Perhaps they're being watched by those who have already gone through it? I guess they could simply be in the DoM fighting in FRONT of the veil, but unless I'm mistaken, you can see the sky in that cover. Not to mention that the sky's ORANGE. Somebody's been watching too much Lost XD Anyway, yeah, orange sky. Whew.
And there's also rubble in front of them. Huh. Notice the medallion around Harry's neck. We'll get to that soon.
UK Adult Cover: Well I think this one's pretty simple.
Golden locket. With a GREEN 'S' on it. Also looks like it opens. If you've read HBP, you already know what it is. And you may also notice that is looks a LOT like the medallion Harry was wearing in the previous cover.
UK Children's Cover: OK, first off... ENOUGH with Ron looking like a wuss all the friggin' time.
Is it just me, or does Hermione look as if she's trying to clutch something that's getting away? Like the gold, for instance XD Okay, okay, that dun make much sense, and Pleti suggested that the trio has fallen into this room, hence their expressions. That is actually a much better explanation XD
But see here... again... no wands. Okay, so there might be a reason Harry ain't carrying his, but what about Ron and Hermione? They shouldn't have any Priori Incantatem problems, right? Also, notice that Harry's hands are all judo chop style. Holy crap man, HP and Matrix crossover XDXD Hells yeah! Okay, bad joke...
Now let us count hands! Three people... SEVEN hands, yay! But wait! Look behind Harry's back! Three people AND one creature! And I think it's safe to assume that the only hand not visible is Ron's left one (prolly trying to steady himself) as both hands behind Harry are grayish. My bet is that the little dude not entirely visible is Dobby. Pleti said it could also be Kreacher. Whereas that would make sense since Kreacher is now under Harry's command, I don't really see Harry be very willing to collaborate with him.
Then again, what if this room is the Black family treasure room? Notice how Harry is NOT wearing the medallion in this particular cover. Taking into consideration that almost all US covers (with the exception of Philosopher's Stone and GoF) have depicted scenes that are close to the end of the book, I'd say the one with Harry and Voldy is pretty far down the book. And that would make sense anyway, not matter what the covers usually show. Which would also mean that the UK cover depicts a scene BEFORE that. Could it be that Harry doesn't have the locket there yet? And if you've read OotP carefully, you'll know the trio found a very old, golden locket in Grimmauld Place while cleaning up. A locket that wouldn't open. And if your theory on RAB is the same as mine, you already know what I'm tryin' to say.
SO! If this treasure room is indeed a place related to the Blacks, it would make sense for Kreacher to tag along. Not to mention Dobby belongs in Hogwarts. Though if there's no school to speak on in DH... Dobby could be free to follow Harry around. I guess we'll just have to wait and see.
Now... You can't possibly have missed the SWORD. We've only read about one sword in the series so far, right? Gryffindor's sword. The one with the RUBIES on it. Now in this pic, there's a bunch of rubies flying all over the place, so it's a bit hard to make sure if said ruby is indeed ON the sword or just one of the numerous others floating around. My guess is that it's indeed on the sword. I mean c'mon, it's REALLY close to the hilt to be random. And it does seem kinda poetic to use Gryffindor's sword against Slytherin's heir.
Also, magnify the image a couple of times, and you'll notice how some of the items in there are ARMOR. More specifically, a chestplate and a helmet. With a dragon on it. Yowza. Could they have JUST found the sword in there? Assuming it really is Gryffindor's it should be hidden within Hogwarts. Unless it gets stolen. Then again, they COULD already have it, but I dunno, the chestplate and helmet are too relevant not to be connected to the sword. I just can't decide if Dobby/Kreacher/??? is holding the sword like someone brandishing it or someone who has just discovered it buried into a pile of treasure.
In conclusion... There's something reflected on Harry's glasses. Could be the treasure... or not. Magnifying doesn't gimme any more hints. And one last thought... could this room also be Harry's personal vault? My guess is no, but you never know.
That's a lot of rambling and it only made me realize one thing. I want to read that book SO bad it hurts x.x But it's also the LAST one. Guuuuuuuuuuuuuuuuuh!!