Scholastic, the US publisher of the Harry Potter books, has released not only the front cover image, but the entire wrap-around artwork by Mary GrandPré (who has illustrated the entire series).
The front cover of the 784-page US edition of Harry Potter and the Deathly Hallows is:

The full wrap-around artwork (minus any cover text) shows that, though Harry is on the front, his archnemesis appears on the back cover. On Scholastic’s web site, there’s a feature letting the viewer enlarge the artwork to search for clues. Let the plot speculation begin:

Bloomsbury, the British publisher, has also revealed its cover art. The children’s hardcover edition is a bit more cartoonish, with Harry’s comrades joining him on the front cover, and no hint of anyone else on the back:

The British adult edition‘s hardcover has the most staid cover of them all:

Fan site The Leaky Cauldron has high-res images of the covers, which include (on the British edition), the inside cover copy, giving a bit more of a hint of the story to come.
“Harry has been burdened with a dark, dangerous and seemingly impossible task: that of locating and destroying Voldemort’s remaining Horcruxes. Never has Harry felt so alone, or faced a future so full of shadows. But Harry must somehow find within himself the strength to complete the task he has been given. He must leave the warmth, safety, and companionship of The Burrow and follow without fear or hesitation the inexorable path laid out for him…
“In this final, seventh instsallment of the Harry Potter series, J.K. Rowling unveils in spectacular fashion the answers to the many questions that have been so eagerly awaited. The spellbinding, richly woven narrative, which plunges, twists and turns at a breathtaking pace, confirms the author as a mistress of storytelling, whose books will be read, reread and read again.”