My predictions:

1 Super Mario Galaxy (Wii)
2 Guitar Hero III (Wii)
3 Mario and Sonic (Wii)
4 Guitar Hero III (360)
5 GuitarHero III (PS2)
6 Call of Duty 4 (360)
7 Halo 3 (360)
8 Rock Band (360)
9 Mass Effect (360)
10 Resident Evil Umbrella Cronicles (Wii)

Me too, I think Mass Effect will easily be in the top 5 in sales.

mass effect and halo 3 will be the biggest selling games in dec/nov

I would have to say:
1. SMG (wii)
2. Guitar Hero 3 (360)
3. Guitar Hero 3 (wii)
4. Mario and Sonic (wii)
5. Call of Duty 4 (360)
6. Mass Effect (360)
7. Assassins Creed (360)
8. Halo 3 (360)
9. Guitar Hero 3 (PS3)
10. Ratchet and Clank (PS3)

Galaxy will own everything for like the next year

I think these are the contenders:

 - SMG
 - GH III  (all platforms)
 - WiiFit (looking at 1-1.5m sales in Japan in Dec alone)
 - Mass Effect (biggest 360 title over holidays)
 - Mario & Sonic (DS version delayed till '08...)
 - CoD (not really sure about this, but it definitely has a chance)
 - RE:UC (strong Japan + US release)
 - Dynasty Warriors 5(?) (Japan release, big, big title - PS3 bundle and all)

I don't believe these titles will make the top#10:

 - R&C, Uncharted (install base, not "harcore" titles? plus doesn't R&C release in October)
 - Assassins Creed (will do well across all titles long term, but will be surprised if any single platform makes the top#10 - maybe 360)
 - Rayman#2 (won't do the numbers, won't sell in Japan)
 - Rockband (definitely not - this will do great *revenue* but crap short-term sales - its just to expensive)
 - Halo3 (already sold most of its units in the US & Japan - might do another 500k in the US, but it will be old news by the time Xmas hits. I might be wrong though - still a chance of being one of the best 360 sellers, but just doubt it will make the top#10..?)

So my top#10 - remember that titles that sell well in BOTH Japan & US have a huge advantage here:

#1 - Super Mario Galaxy (Japan, US)
#2 - Mario & Sonic (Wii) (Japan, US)
#3 - Mass Effect (360) (US)
#4 - Call of Duty (360) (US)
#5 - WiiFit (Wii) (Japan)
#6 - Guitar Hero III (Wii) (US)
#7 - Guitar Hero III (360) (US)
#8 - Dynasty Warriors (PS3)
#9 - Guitar Hero III (PS2) (US)
#10 - Halo 3 (360) (US?)

Something like that anyway. DS titles excluded, WiiPlay/WiiSports/WiiZapper excluded. I think WiiZapper will *easily* make the list - maybe be #1 - if included. 

I'm sure some big titles have been missed - not sure what though. Madden on PS2/360 might (?) creep in, etc.

Also - "The Simpsons" will be huge (across all platforms), but not sure when its releasing. Not sure if a single platform will make top#10. 

If any PS3 title makes the list - it will be Prologue. I might slot it in at #10 on my list. I wonder if people have forgotten about this.

PS3: Shin Sangokumusou
Wii: Super Mario Galaxy
360: Guitar hero

 Tough one, it depends on how well GH doe sin Japan, but I think GH combined will sell more than SMG.

any chance of galaxy not getting #1?

1. super mario galaxy (wii)
2. guitar hero 3 (360)
3. guitar hero 3 (wii)
4. mass effect (360)
5. call of duty 4 (360)
6. guitar hero 3 (ps2)
7. wii fit (wii)
8. halo 3 (360)
9. mario & sonic at the olympics (wii)
10. guitar hero 3 (ps3)

The Americas and Japan only, only current gen, no handhelds, no packed in Wii Sports and no Wii Play taken into account.

1. Super Mario Galaxy (Wii)
2. Mass Effect (360)
3. Call of Duty 4 (360)
4. Guitar Hero III (Wii)
5. Guitar Hero III (360)
6. Wii Fit (Wii)
7. Halo 3 (360)
8. Mario & Sonic at the Olympics (Wii)
9. Ratchet and Clank (PS3)
10. Wii Sports (on Japanese sales alone)

I don't have any doubt SMG will be the best selling game in that period. I think it will be the best selling game in the november/december period in Both the Americas and Japan and together the gap with number 2 will be huge.
I wouldn't be surprised if Guitar Hero Wii manages to outsell its 360 counterpart, although it will probably be close either way. Mass Effect and CoD4 I think will be the other 2 big titles for the 360 this holiday. Halo 3 will be further down simply because it will be released for 5 or 6 weeks already before the period we are counting even starts and sales will almost only come from new 360 owners.
Wii Fit will be big in Japan, and with holiday sales going through the roof I assume Wii Sports will also go up high enough to reach this top 10 on Japanese sales alone. Ratchet and Clank can make the top 10 because they appeal to both areas, as opposed to many other titles in the list.

Edit: Considering GH III's first week sales will not be a part of the period I made some adjustments to my top 10.