Currently Online 
Punch-Out! will do well. The marketing campaign is fantastic, it has tons of nostalgia, and it's easy to pick up and play (will be a great party game). Like Mario Kart it will please core and casuals alike. It won't be a monster hit like Mario Kart, but I expect it to sell very well over time.
I'm calling it now too -- Super Mario Bros. Wii at E3. Running off the Galaxy engine out this fall.
Wii Fit Plus as well.
If Nintendo ever feels like their hardware projections are in danger of not being met there's a pretty simple solution -- $50 price cut. It's long overdue anyway, and it would demolish every sales record for the 2nd half of the year.
The Wii will be back to 500k-600k a month in North America soon enough. I really feel the main reason why it didn't do that last month was because of the DSi launch actually impacted the Wii. PS3/360 do not impact the Wii at all (as proven by the various 360/PS3 price cuts and GTAIV and Halo 3 launches doing nothing to the Wii), but the DS can because it has a similar kind of appeal even if it isn't a home console.
With MotionPlus, the best thing they can do for the future is to make all Wiimotes starting in the 2nd half of 2009 simply come with WM+ built in. Similar to how Sony phased out their first PSX controller for the Dual Shock with the first Playstation. Nintendo has not release colored Wiimotes yet (blue, black, pink, etc.) ... when they do, make all those WM+ standard.
