In case you don't already know the last cover has been released:

http://news.bbc.co.uk/1/h...503683.stm

SPOILER ALERT (well my guess anyway)
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In the last book there is a reference to Voldermort coming back to the school to ask for a job, although it was revealed by Dumbledore that the Dark Lord didn't actually want the job. During the recall of this memory in the pensive Harry notices a slight movement by Voldermort and perhaps later during the drinking of the potion some sense of regret by Dumbledore. So my guess is that (I don't have the book for reference though) the relic of Grifindor is the sword in Dumbledore office and is one of the Horcruxes.

Anyway looking forward to the last book.

There is already a thread http://www.prince.org/msg/100/222351