Nintendo said last year that the Mario and Zelda development teams were working on new Wii games, so it's already a given that we'll be seeing new games in those franchises soon. According to Japan's Nikkei newspaper, that "soon" means "later this year". For Mario, at least.
The Nikkei report was a bit vague on the subject, but apparently Nintendo plans to release a new Mario game by the end of the year. The question here is whether it'll be a major Mario game or not.
Another new Wii game mentioned in the report was Wii Fit Plus, an online-capable follow-up to the bestselling Wii Fit. The paper was more specific about the details for this game, mentioning that the online feature will let users compete with friends and family, presumably by sharing and comparing fitness data. Wii Fit Plus will also feature more accurate measurements.
Chances are, both games will be in the spotlight during Nintendo's E3 2009 press conference, so hopefully we'll learn more on Tuesday.