I don't like putting exact numbers on that (or ballpark, whatever), I like percent of total consoles sold better.
Wii: 40%
XBox 360: 35%
PS3: 25%
200million seems like a decent total of console:
Wii: 80m
360: 70m
PS3: 50m
I know time plays a factor in this but at the current state and with a few guesses on what I think is going to happen, this is what I see. There are a few things that could really upset this (like the 360 dropping to $200 which I don't think will happen) but if the unexpected things happen, I'll gladly update my numbers.
One of the big reasons why I think the PS3 will sell below the 360 is because I think the PSN is going to become a pay service sometime early to mid 2008 and a lot of people won't pay for both services. I think the 360 will win in that aspect because it simply has the previous install base.
I'm also setting the PS3 the lowest because it will never be below $450 in time to catch up to the other two consoles. By the time it drops below that price, the 360 and Wii will already have had price drops and it just won't catch ground quick enough. As for Blu-Ray, things are looking good for it (as far as next gen media format), but dedicated Blu-Ray players are going to be cheaper than the PS3 and people are going to think about getting a dedicated Blu-Ray player to watch movies before thinking about a PS3.
I'm putting the Wii on top because gamers are embracing it so well and developers see that. Games are going to start getting announced within the coming months and, just like the DS, breakaway hits from new and old IP's will start appearing. Six months ago I would have said that the 360 was going to come out on top but the Wii has really impressed me.
