If you want to find out the new title for Book Seven then go to JK Rowling's site and search very carefully!
It's
here ^_^
♥
Also Huge spoiler alert! Don't read any comments below if you want to find out everything by yourself or if you don't want to know the title.
For those people who are like me and don't hear a bell ringing when they read 'spoiler' this is the alarm going off! Don't read any comments!
ETA some thoughts behind the lj cut.
A small theory on the Deathly Hallows (based on the comments and the included links below):
The 'Deathly Hallows' might be objects to give Voldemort the power to rule over the wizarding world. The 'deadly' part could refer to the way they are related to how Harry might kill Voldemort.
The possible Hallows from the founders of Hogwarts are:
Slytherin - locket
Ravenclaw - wand
Gryffindor - sword
Hufflepus - cup
The cup and locket are known to be horcruxes, but the wand and the sword might have been kept safe.
Other Horcruxes are the diary, the ring and Nagini.
Perhaps Harry needs to destroy the horcruxes to end the immortality but also find the Hallows to kill Voldemort?