According to Cory Barlog the creator of God of War they haven't even started to develop GOW3. I don't believe this has been mentioned here yet. Oddly he's working on what he calls a Family Ties RPG, if that's not a joke that is. Who knows it might be interesting, but I'm guessing Sony fans would rather see GOW3 instead.
Now because of this I hope I don't keep hearing GOW3 being mentioned as a reason the ps3 will sell well. I'm sure they will make it but if they didn't start yet the earliest the very earliest you'll see it is Winter 2009.