http://www.konami.jp/kojima_pro/nextDuring Kojima's GDC panel, he informed everyone that there would, in fact, be a new game unveiling at E3. And from the looks of things, he is definitely holding up to his word.
Several press outlets have mentioned receiving a mysterious e-mail from within Konami, including only a message stating "T-3 days" and a link to a dead Kojima Productions webpage
Source: http://www.metalgearsolid.org/
Project S? ZOE3? Next Metal Gear? A New IP? On Friday, we're going to find out!