Before Wii/DS the list was as this (top 10 best sellers)
1. SMB (NES) 40.24M
2. Pokemon Red/Blue (GB) Pokemon Red/Blue 33.33M
3. Tetris (GB) 30.26M
4. Duch Hunt (NES) 28.31M
5. Pokemon Gold/Silver (GB) 23.11M
6. SMW (SNES) 20.61M
7. SM land (GB) 18.14M
8. GTA:SA (Ps2) 17.48M
9. SMB3 (NES) 17.28M
10. The Sims (PC) 16.08M
NES - 3 titles
GB - 4 titles
SNES - 1 title
Ps2 - 1 title
PC - 1 title
And by generation
3rd gen - 5 titles
4th gen - 3 titles
5th gen - 1 title
6th gen - 1 title
Looked like fewer and fewer games were able to sell a lot. Now, after this gen, I believe we will see something around this.
How I believe the list will be (reasoning after the list).
1. Wii Sports (Wii) number doesn't matter - it is first.
2. SMB (NES) - 40.24M
3. Wii Play (Wii) 33-40M
4. Wii Fit (Wii) 33-40M
5. Pokemon Red/Blue (GB) 33.33M
6. Nintendogs (DS) 30-33M
7. Tetris (GB)- 30.26M
8. Duck Hunt (NES)- 28.31M
9. Pokemon Gold/Silver (GB)- 23.11M
10. NSMB -(DS) 20-23M
NES - 2 titles
GB - 3 titles
DS - 2 titles
Wii - 3 titles
So by generation.
3rd gen - 4 titles
4th gen - 1 title
5th gen - 0 titles
6th gen - 0 titles
7th gen - 7 titles.
Reasoning.
1. Wii Sports (Guaranteed 50M +)
2 + 3rd + 4th SMB/Wii Play/Wii Fit
Wii Play does now only sell 1/3 of the number of consoles sold on a weekly basis. The Wii would need to sell over 100M to make it beat SMB (no, not 120M, as Wii Play is higher on AR now than 1/3).
Wii Fit is huge, but it is not certain how long it will last. Still, it is likely that both Wii Play and Wii Fit will break 33M.
Nintendogs is possible too, but that depends on how much longer the DS' life is.
5th + 6th + 7th. Nintendogs/Pokemon Blue/Red and Tetris
Nintendogs is still selling 50-100K weekly. It "only" needs 13M more to get to Pokemon. Still, Nintendogs is slowing down, and sold a totally crappy 3M so far this year. This means that is should be selling 4-5M a year. I thus think that it should beat 30M, but 33M might be too much. Of course, Nintendogs could end 7th
8th. Duck Hunt - no question about it. Possibly Wii Fit/Nintendogs could get a sequel or something or stop up completely and sell 28M "only"
9th/10th. Has to beat Pokemon Gold/Silver (23M) and Super Mario World (20.61M)
NSMB is at 16.21M. Sells good overall, and should manage to overtake SMW. It is unlikely that it will make 23M though, and if another title beats NSMB and sells more than it, NSMB will not make it.
About (16.31M) the same as NSMB, but I don't think it will manage to beat NSMB in the long run, and does thus not have a change of entering the top 10.