Brandon Sanderson has Tweeted that the final Wheel of Time novel, A Memory of Light, is about one-third done. He's caught up with some material he worked on whilst working on the first leg of the final three books back in 2007-09, and the percentage completed bar on his website should move up significantly in the next week or so.
A Memory of Light is currently planned for release in November 2012. Tor have also recently announced that Michael Whelan will be creating the cover art for the e-edition of the series, though Darrell K. Sweet will be providing the hardcover image for the sake of uniformity with the earlier books in the series.
EDIT: In a further Tweet, Sanderson confirms that he hopes to turn the book in to Tor in November this year.