No one mentioned a specific territory, so by default it is worldwide...

Guess 1 = 2,200,000 Robmate
Guess 2 = 1,900,000 Neos
Guess 3 = 1,675,000 Rendo
Guess 4 = 2,800,000 El Duderino
Guess 5 = 1,350,000 Nth
Guess 6 = 2,000,000 Hunter_alien
Guess 7 = 2,500,000 Friedtofu
Guess 8 = 2,100,000 Alexie Di Onie
Guess 9 = 2.387.257 Wolfenstein
Guess 10 = 3,000,000 elnino334
Guess 11 = 5.600,000 konnichiwa
Guess 12 = 3,200,000 FJ-Warez
Guess 13 = 2,750,000 Vengi
Guess 14 = 3,000,000 NJ5
Guess 15 =
Guess 16 =

Guess 1 = 2,200,000 Robmate
Guess 2 = 1,900,000 Neos
Guess 3 = 1,675,000 Rendo
Guess 4 = 2,800,000 El Duderino
Guess 5 = 1,350,000 Nth
Guess 6 = 2,000,000 Hunter_alien
Guess 7 = 2,500,000 Friedtofu
Guess 8 = 2,100,000 Alexie Di Onie
Guess 9 = 2.387.257 Wolfenstein
Guess 10 = 3,000,000 elnino334
Guess 11 = 5.600,000 konnichiwa
Guess 12 = 3,200,000 FJ-Warez
Guess 13 = 2,750,000 Vengi
Guess 14 = 3,000,000 NJ5
Guess 15 = 1,900,001 Shadow)OS
Guess 16 =
Guess 17=

Hmmm.... 1.5 million preordered... I wanna say 1.9 million for the first week, but that guess is taken. I'm gonna have to say 1 900 001, Bob.

3,500,000

I predict 2,000,001 units.

This way I beat the 2M people, but won't be too far off if it's less. =P

Guess 1 = 2,200,000 Robmate
Guess 2 = 1,900,000 Neos
Guess 3 = 1,675,000 Rendo
Guess 4 = 2,800,000 El Duderino
Guess 5 = 1,350,000 Nth
Guess 6 = 2,000,000 Hunter_alien
Guess 7 = 2,500,000 Friedtofu
Guess 8 = 2,100,000 Alexie Di Onie
Guess 9 = 2.387.257 Wolfenstein
Guess 10 = 3,000,000 elnino334
Guess 11 = 5.600,000 konnichiwa
Guess 12 = 3,200,000 FJ-Warez
Guess 13 = 2,750,000 Vengi
Guess 14 = 3,000,000 NJ5
Guess 15 = 1,900,001 Shadow)OS
Guess 16 = 3,500,000 Stevetrop
Guess 17= 2,000,001 Parokki
Guess 18 = 2,999,999 Quarashi

Guess 1 = 2,200,000 Robmate
Guess 2 = 1,900,000 Neos
Guess 3 = 1,675,000 Rendo
Guess 4 = 2,800,000 El Duderino
Guess 5 = 1,350,000 Nth
Guess 6 = 2,000,000 Hunter_alien
Guess 7 = 2,500,000 Friedtofu
Guess 8 = 2,100,000 Alexie Di Onie
Guess 9 = 2.387.257 Wolfenstein
Guess 10 = 3,000,000 elnino334
Guess 11 = 5.600,000 konnichiwa
Guess 12 = 3,200,000 FJ-Warez
Guess 13 = 2,750,000 Vengi
Guess 14 = 3,000,000 NJ5
Guess 15 = 1,900,001 Shadow)OS
Guess 16 = 3,500,000 Stevetrop
Guess 17= 2,000,001 Parokki
Guess 18 = 2,999,999 Quarashi
Guess 19= 2,000,000 W29

Guess 1 = 2,200,000 Robmate
Guess 2 = 1,900,000 Neos
Guess 3 = 1,675,000 Rendo
Guess 4 = 2,800,000 El Duderino
Guess 5 = 1,350,000 Nth
Guess 6 = 2,000,000 Hunter_alien
Guess 7 = 2,500,000 Friedtofu
Guess 8 = 2,100,000 Alexie Di Onie
Guess 9 = 2.387.257 Wolfenstein
Guess 10 = 3,000,000 elnino334
Guess 11 = 5.600,000 konnichiwa
Guess 12 = 3,200,000 FJ-Warez
Guess 13 = 2,750,000 Vengi
Guess 14 = 3,000,000 NJ5
Guess 15 = 1,900,001 Shadow)OS
Guess 16 = 3,500,000 Stevetrop
Guess 17= 2,000,001 Parokki
Guess 18 = 2,999,999 Quarashi
Guess 19= 2,000,000 W29
Guess 20= 1,700,000 USA - 2,400,000 WW - ssj12

Well, my prediction was squashed. Estimated sales have already stated that Halo 3 have reached 1.8 million sold in the first 8 hours.

I just hope this hurrys up and ends. I'd like to not have every commercial on television being HALO 3!!! related. :P

Edit!: 1.5 million of that was the pre-orders. Those have already been cleared out and GONE. The only additional purchases for this opening day so far are just over 300,000. 

I'm going with 3.25 million copies FTW - if Madden sold nearly 900K, I can easily see Halo 3 hitting 1.5 million copies in addition to preorders.

I think it will sell 4 units.