you guys are forgetting the possible chance of another halo on 360 which could easily take the third spot

Halo 4 has the potential to top that list once it gets released in the distant future. But we won't see it before the end of 2009 so its best to deal with the present sales situation first.

Resistance 2, Killzone 2 and COD5 seems likely.

Gears 2 will have the best shot at 3rd in the near future.

I came in here ready to fight and say it's Portal and I'll cut anybody who disagrees.

But oh, you're going by sales.

My guess is CoD5. Shooters have been getting better and better on the Wii, and now CoD4 brought mad brand recognition, and it's on PS2 and PC and watches and toasters.

I agree that 1 and 2 are pretty safe. I see COD5 having the best chance to supplant Gears, though I think Gears is safe.

CoD 5 could well take 3rd, but I think 6 will take the crown next year. Resistance and Killzone will probably sell close to 3-4m, but not quite 5m

I agree with your ordering, pretty much.  If I could put Gears of War1 on the list, I'd put it at #3, just under GeoW2.  I don't think Resistance or Killzone 2 can push over 5mil - Resistance might, but GoW's PC sales should give it the edge (assuming it sold reasonably).

I think R2 should exceed the total of R1 and push up to nearer Gears of War 1's sales numbers like you said but Killzone 2 comes out at a bad time for sales so it may struggle a bit to reach as high numbers as R2.

Call of Duty 6 definately has that potential to really move units, the question is can they still maintain a competitive advantage over the other shooters released between now and then?

Well for my money, CoD 4 is still by far the best FPS avaliable, and I think R2 (and Gears if you count it) will still be its main competition, unless there is another Halo FPS released. If they make a gmae which has an online game nearly as addictive 4, and just make a longer SP it will sell tons