Honestly, I think I'm going to put my money in the Wii Fit basket.

1. Wii Fit
2. Brawl
3. Mario Kart Wii

(For the end of 2008).

SSBB already most likely reached its sales peak. MK I guess is there but coming down. Wii Fit will have its biggest chance in North America.

See SSBB sold 2.5 mil worldwide in one week excluding Others. Thats the best chance of getting more sales in.

MK sold 2.3 mil worldwide including Others. In addition, the sales plummets down rapidly toward week 5. That probably tell you that MK is much out of the race(but I still like it).

Wii Fit sold almost 1mil excluding America. America I can tell is going to give atleast 1mil the first week and up to 3mil in 5 weeks. However, when holidays come all 3 games here will pick up in sales.

Agh, that's so annoying. I typed up a really long post and accidentally clicked the cancel button. Ahh well, here are my choices, explanation or not.

1. Wii Fit

2. Grand Theft Auto IV

3. Mario Kart

4. Super Smash Bros. Brawl

Total sales so far:

Brawl: 5.36 + likely bonus from launch in Europe = 2M (early on, sales that the other won't gain) = about 7.5M.

Mario Kart Wii = 4.3M

Wii Fit 3.29M + likely bonus from America first weeks = 2M = about 5.5M

Prediction: Remember, averages include holiday boosts.

Brawl: Legs have started to dry up in Japan, total average including holidays will be around 7K/week, or 210K abouts. America should see 50K/week for the rest of the year, totalling 1.5M. Europe should be big, with 1.5ish in first 5 weeks, and then 50K/week for the rest of the year, totalling 2.2M. Total: 11M

Kart: Still selling heavily in Japan and Europe, should sell 75K + for quite some while in both places, average might be 40K/week Europe and 30K/week Japan, making total sales for both those 2.1M. America should see half a mill within the next 5ish weeks, and then 40K/week for the rest of the year. Total sales here 1.6M. So total overall: 8M

Wii Fit: Should keep 40k/week in Japan, totalling 1.2M. Europe should average close to 80K/week, making sales 2.4M. America could launch with 2M during first 5 weeks, and then sell 100K/week for the rest of the year, totalling 5M!Total: 14M

So my prediction:
Note: I have subtracted totals a bit, as my assumptions were rounded up most of the time.

1st. Wii Fit 12.5M
2nd: Brawl 10.5M
3rd MKWii 7.5M

sulima, wii fit in japan was bought by 1/3 wii owners there and in america there is huge hype and even bigger demand for this game so i guest that by the end of 2008 more than 1/3 wii owners will have their own copy of wii fit(in america it can be even more than 1/2 wii owners). and at the end of 2008 there will be about 40mln wiis on the market. 

Wii Fit
Brawl
MKWii

I will add some numbers later when I have time.

Wii Fit is easier to produce then the Wii, so while I expect shortages it will be more in line with the Wiimote then the console. eg. in 3 -4 months it will be easy to find one even in the US.

I don't think Nintendo will be able to produce enought Wii Fit, so I think they will end like this
SSBB
MK
Wii Fit

Wii Fit
Brawl
Mario Kart

Wii Fit
Brawl
Mario Kart

1-Fit
2-Kart
3-Brawl