Coming from Japan's Nihon Keizai Shimbun newspaper, we hear rumblings of a new Mario game destined for Japan sometime this year, and that we should expect to hear about this game during E3 this week. It's a fairly credible rumor, considering Nintendo admitted that the Mario and Zelda teams were working on something last year. Nihon Keizai Shimbun also says this is a title destined for Wii (sorry, DSi fans!).
Considering it's been a year since we've heard what little we have, it would make sense that Nintendo would be ready to unveil something at this year's show.