The cover art for Harry Potter and the Deathly Hallows has today been released - Here for the
US version, here for the
UK children's version , here for the
UK "adult" version .
(speculation ahead, you may not want to read if you haven't read up to six yet)
***possible spoilers***
The US version clearly shows us Harry and Lord Voldemort, oddly wandless, in what I can only assume is the final confrontation. Harry has a circular object tied around his neck - my guess is that this is the locket of Salazar Slytherin, the horcrux he failed to obtain at the end of Half-Blood Prince.
For the two UK versions, it's difficult to really glean anything from the children's cover - it shows Harry, Ron and Hermione in a fantasy treasure trove. A small hand, possibly that of a house-elf, appears to have a sword, and interestingly they are in front of a stone arch. Could this be the arch that Sirius Black was thrown through in the Department of Mysteries in Order of the Phoenix? Also, there appears to be an orb containing a snake on the other side of the cover. From my knowledge of the Potter universe, I think the most likely thing this is to be is a prophecy.
The UK "adult" (read: for blokes who are too chicken to read a brightly-coloured book in public) version shows what is, quite simply, Salazar Slytherin's locket. It clearly is integral to the plot. That's all there is to say on that.
Also, the length of the UK version was released today: 608 pages, which is almost exactly the same as Half-Blood Prince, which was 607 pages.